Binoculars Conjoin Marieme and Ndeye prepare to open Cardiff Nursery

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Marieme and Ndeye, twins from Senegal gathered, are preparing to open a full-time nursery in their new house, Cardiff.

Initially we did not expect to live more than a few days, they were taken by their father to the UK in the hope of a better life.

Now three years old, girls continue to surprise doctors with their progress.

But they discovered that girls' circulatory systems are much more closely linked than previously thought – so it's now impossible to separate them.

• Meet Marieme and Ndeye
• The battle to separate Safa and Marwa

This also explains why they continued to prosper for so long.

"Doctors now know that they are a unique and complex case," said their father, Ibrahima Ndiaye.

"They are very connected internally and that explains why they exceeded all expectations.

"They work together to stay and stay alive and the situation is a bit more optimistic."

The new discovery has changed things for girls.

In January, surgeons at Great Ormond Street Hospital in London were considering a separation attempt, which Ibrahima did not want because of the risks involved.

But new findings show that no twins could survive without each other and that separation is now impossible.

Girls have separate hearts and spines, but share the same liver, bladder and digestive system.

Gillian Body, pediatrician consultant at the Noah Children's Hospital Wales Wales, said: "Girls are doing very well.

"They experience a period of stability and constantly surprise us with their progress.

"Last year, we thought Marieme was very dependent on Ndeye, but the latest CT scans show that they depend on each other to stay alive.

"In the long run, that means they can not be separated, but in many ways it's nice that both of them are addicted.

"It's a big turnaround – before that, ethics was about knowing if we could and should separate them, but now we know this decision is no longer on the table.

"They are now looking forward to being placed at school and I hope that they will enjoy being children."

"So much joy"

Although girls' health is still variable and their condition is described as "life limiting", this period of stability allows Ibrahima to focus on their future.

"My daughters continue to grow up and bring me so much joy," he said.

"Their speech is moving forward and they can move forward with greater independence.

"When Ndeye sees me doing the dishes, she says 'poor daddy', which makes me laugh so much.

"And when Ndeye cries, Marieme will turn to her and say," Hush, noisy. "

Currently, girls attend a playgroup a few hours a week, but from September they will go to nursery five mornings a week.

Ibrahima said, "This is another chapter that opens and brings hope.

"It does not let you forget the situation, but I learned that as you celebrate, you should celebrate and see a bright future.

"I can imagine that it may be an emotional day to see them dressed in their uniforms when I thought so often that this day might not happen.

"I want people to know this success because, although we are a private family, many people ask for their news and take the girls to heart."

In addition to caring for girls, Ibrahima hopes to create a charity to help other disabled children.

"With this situation and all that we have experienced, I can not turn a blind eye to other children with disabilities and complex needs."

"So I create a foundation for girls, in collaboration with the Ty Hafan Children's Hospice, called Conjoined Destiny.

"If the situation gets worse and they do not resist, I want to put in place a system that allows them to leave a mark on the world, despite our modest and difficult beginnings.

"And if they grow up to see it, they will know how useful their lives have been to them."

The Conjoined Twins: An Impossible Decision Is On BBC Two At 9:00 PM BST On Monday and on the BBC iPlayer.