When passers-by see Jo Bartle and Stephanie Burns pushing their two children in a double buggy, they would be forgiven for seeing nothing more than two proud mums out for a walk with their respective babies.

But the truth is rather more remarkable than first meets the eye.

Jo and Steph are a lesbian couple. Thirteen months ago, Steph gave birth to baby Elijah. Three months later, her partner, Jo, had little Martha in the same hospital.

They chose the names together. Now they declare that they (each) consider themselves mothers of both babies.

The babies are indeed genetic siblings. Both were conceived with the help of a syringe and a “donation” of sperm from the same man.

The father? A drag queen the women met in a nightclub, whose recompense for getting them both pregnant was a cheap flight to Gran Canaria.

Just to confuse matters, “Daddy” sometimes pushes the buggy, too. Ryan Egeley, a 23-year-old gay man, never wanted to be a hands-on father, but he did rather fancy the idea of being able to flit in and out of his children’s lives when it pleased him. This set-up suits him perfectly.

“They are very lucky children,” says Jo, 40, who has an astonishing capacity to see only the positives to their situation.

“In effect, they have three parents who love them - two mummies and one daddy.”

Let’s hope, for their sakes, little Elijah and Martha appreciate their unconventional parentage, for there is no doubting that their “mummies” make a deeply unconventional couple, not least because Steph is 17 years younger than Jo.

At the family home in Doncaster, chaos reigns. Both women have full-time jobs - Jo is a social work assistant and Steph works as a logistics administrator in the NHS - and juggling them with motherhood is no mean feat.

On top of all this, Elijah and Martha actually have another sibling. Three-year-old Jonah is the product of one of Jo’s previous heterosexual relationships (his father is no longer on the scene). He calls Jo “Mummy” and Steph “Mama”.

All three children might have the most traditional of names, but theirs is an all-too-modern existence, which inevitably raises eyebrows.

Just this week, Jo found herself having to explain how it all works to a confused child at the nursery her children attend.

“This little boy was sitting at a table with Jonah and he asked where Jonah’s Daddy was. I said Jonah didn’t have a Daddy but he had two Mummies instead.

“I’d been steeling myself for these sorts of questions, so I was prepared. I said: ‘I think that’s very nice, don’t you?’ He nodded and said, yes, he thought it was very nice to have two mummies too.”

She’s under no illusions that such easy acceptance will be universal - but insists that whatever hardships her children are going to face as a result of her lifestyle will be worthwhile.

“Some people will think what we are doing is disgusting, and they are entitled to that opinion, but I believe we’re giving all the children the best possible start.

“There will always be those who don’t believe that gay people should have children, but that is their problem, not ours.

“Our children have as much love as any child could need - more, actually, because there are more people in this equation to love them. How could they not benefit from that?”

But this is a troubling story - not because it involves two women having a family together, but because of the frankly slapdash nature of how they came to be in this position.

For Jo and Steph didn’t sit down some years back and work out how best to bring children into this world.

The children were not an expression of their love. In fact, they were not even in a relationship when Steph fell pregnant.

Rather, they were two single lesbians sharing a house - and a sperm donor - and supporting each other in their bids to be single mothers. Their explanation is that they fell in love while they were both pregnant - united by the admittedly unusual bond of giving birth to a half-brother and sister.

“I looked at Steph just after she had given birth to Elijah and I was blown away by my feelings for her,” is how Jo puts it.

“I realised this was about more than me helping my friend have a baby. It was about wanting to create a family with her.”

No sooner had Steph discovered she was pregnant than Jo too announced she was expecting - all thanks to the efforts of the same sperm donor - a flamboyant man with a penchant for sequins.

Can love really blossom in such circumstances? More importantly, can a stable family unit really be created? Jo and Steph say yes.

“We had children together and we fell in love - it’s just that we did things in reverse order to most people,” explains Steph.

“We have a strong relationship. We adore each other and we adore our children. We are so very lucky.”

Of course, it will be an awfully long time, however, before any child in this household is old enough to understand what has gone on.

But, for Jo, this does not matter. The important thing is that she is a mother. She says she had an extraordinarily unhappy childhood.

Her parents split when she was three and she describes her mother as a “monster” who didn’t love her. She was determined to do better.

“When Jonah was born, I just sobbed my heart out, determined to give him everything I hadn’t had. I took on three extra jobs to buy him everything he needed. Three days after he was born, I took him on a shopping trip and bought him a Burberry outfit.’

It’s a peculiar thing to cite as evidence of great mothering skills, but Jo is clearly a devoted mum. Money was tight, though, and during her pregnancy she had taken in Steph as a lodger - a young woman she’d met, who was also a member of the gay scene in Doncaster, and who helped her through the pregnancy. She was at Jonah’s birth in August 2003.

Two years later, Jo was broody again.

“I looked into having IVF, but it was all so expensive, and the one clinic I did go to was a bit off about treating single lesbians. The whole fertility thing is biased against the gay community.”

She took matters into her own hands, and set out to find her own sperm donor. It seems any concerns over producing more children without a father figure - or, indeed, over health risks, such as possible hereditary abnormalities in the donor - were overridden by her desire to have a child alone.

Steph, too, was only too keen to help - coming up with endless suggestions about possible candidates.

They first tried to inseminate Jo with the help of a man of their acquaintance who came round and passed on his ‘donation’ with the help of a syringe. But to no avail.

“After a year, I went to the doctor, who was horrible to me. He told me that I should give up on the idea and be grateful for the fact that I had one healthy child,” says Jo.

“I was devastated. I came home and cried and cried.”

It was at this point that Steph confessed she was broody, too - and now wanted a baby for herself.

Both women seem startled by the suggestion this was in any way peculiar.

“I didn’t see it as Steph muscling in at all. I understood she was driven by the same sort of desire to have a baby. And I wanted to help her as much as she wanted to help me,” says Jo.

So Jo went charging off to find a sperm donor who would be prepared to help them both - and lo, young Ryan sashayed into their lives. The 23-year-old - a regular on the gay scene - was a little camp even by their standards, but his youthful good looks had them convinced.

“He was one of those guys who always looks immaculate and is always the centre of attention on the dance floor,’ says Jo admiringly.

“I had talked to him, and he seemed like a lovely bloke.”

“A mutual friend mentioned that he’d said he would love to have kids, but it was unlikely to happen, so we instantly thought “Ah-ha”.

“I called him up and said: ‘Ryan, we’re about to have what will probably be the most bizarre conversation you’ll ever have on the phone’. I told him that Steph wanted to get pregnant. Actually, that we both did. He screamed, and said yes immediately. He said he’d always wanted to be a Daddy.”

It all seems a bit, well, random, but Jo insists that the process was well planned.

“We talked about how much he would be involved with any child. He said he was young and wanted to travel, so he probably wouldn’t be around much at first, but that one day he would like to be involved with any children he fathered.

“It was a dream for us. I liked the idea of having a man in the child’s life - but not actually living with us.”

When it came to talking finances, Ryan insisted that he did not want payment for his sperm - which sealed the deal.

“It’s only afterwards that I insisted on paying for his flight to the Canary islands, where he’d got a job as a drag act. He’d made our dream come true - we wanted to help him out with his,” says Jo.

The way they tell it, everyone emerged as a winner. Steph was first to be inseminated with Ryan’s sperm, using a syringe, and to general astonishment fell pregnant immediately.

“It was such a shock,” she remembers. “I texted Jo at work to buy a pregnancy test. I was shaking when I did it. When I saw it was positive, I immediately felt guilty - because of Jo - but she was so happy for me.”

By now it had turned into something of a game. “Ryan said - ‘now let’s get you pregnant’,” recalls Jo, with a giggle. “I don’t think I really thought it would happen, but we tried again the next month. And the one after that.”

Just as Steph was starting to think about maternity gear, Jo did indeed fall pregnant. The pair recall how they ran around their house whooping.

“We called each other Teletubbies when our bumps started showing. It was wonderful to share it all. We’d talk long into the night about names, and how we would bring these babies up.

“We still weren’t a couple then, but I suppose that closeness was building. By the time it came to Steph giving birth, I knew I loved her. When she held Elijah in her arms I thought - ‘this is my family’.”

But did it not come as a shock to Ryan, who thought he was simply helping out two single lesbians, that he was actually helping them create an entire family? “I think he knew, even before we did, that we would end up together,” says Jo. “It was probably clear to everyone.”

By the time the babies were born, Ryan was off doing his outrageous cabaret act in foreign parts, but he kept in touch with them by phone.

At Christmas, when his babies were six and three months old respectively, he saw them for the first time, and - in yet another twist to the original plan - decided that he wanted to move back to the UK so that he could play some part in their lives.

“He even looked after them on his own for two days,” reveals Jo.

How did he cope? Hard-living drag queens aren’t usually renowned for their burping skills. Jo laughs.

“When we came back he looked shattered and he said he’d never smoked as many cigarettes in his life, but actually he’s great with them.”

And so it has continued. Happily ever after, according to all concerned. The women share all the parenting responsibilities, Ryan visits when he can and - as a bonus no one expected - his extended family, who live nearby, have embraced the idea and pitch in with babysitting.

Both Jo and Steph seem to have found the extended family they clearly craved - quite by chance.

And yet it is hard not to be sceptical. The whole situation seems like a timebomb waiting to explode. Legally, there cannot be two mothers with equal rights over all the children. Then there is Ryan - what is his position in law?

The two women have no plans to enter into a civil partnership - not that that would offer much more security - and seem worryingly blasÈ about the issue.

“It doesn’t matter. All that matters is that our children have lots of people who love them, and all we want is the very best for them,” says Jo.

“Nothing is for ever. I’m not going to sit here and say that Steph and I will still be together in ten years because no one can ever say these things.

“But we know how we feel, we have talked about what would happen, and we agree that whatever happens Elijah and Martha are brother and sister, and will always be part of each other’s lives.”

She remains convinced that her children are luckier than most.

“There can be no doubt about how much they were wanted. We can say to them, hand on heart, that they weren’t just ‘accidents’. They were planned, and they are surrounded by more love than they will ever need.”

But what of the story about how they came into this world. Is that really one any child needs to hear?