They are the rarest of all conjoined twins with separate heads and bodies above the waist but just one torso – a trillion-to-one phenomenon.
When they were born 22 years ago, their parents were warned the girls would probably not survive a day.
But the cheerful pair have been through school, graduated, learned to drive and look forward to a full and happy life.
Abby and Brittany have managed to stay out of the spotlight in a sleepy town in Minnesota, US.
But they are about to become international celebrities with their own reality TV show.
Abby and Brittany which airs in the States this month, follows the twins as they graduate from university, start looking for jobs and travel to Europe.
They hope it will prove they are totally different people with unique personalities, who share dreams of marriage and having kids of their own.
But don’t ask them about boyfriends just yet.
Brittany, the joker of the two, says: “The whole world doesn’t need to know who we are seeing, what we are doing and when we are going to do it.
“But believe me, we are totally different people.”
Abby, the feisty stubborn one, adds: “Yeah, we are going to be moms one day, but we don’t want to talk about how it’s going to work yet.”
But it’s certainly going to take a lot of working out when they do.
The girls are dicephalic parapagus – fused side-by-side with two heads – twins and only a few sets in history have survived infancy.
They have two spines fused at the pelvis, two hearts, two oesophagi, two stomachs, three kidneys, two gall bladders, four lungs – two are joined– a liver, one ribcage, a shared circulatory system and partially shared nervous systems.
From the waist down, all organs, including the reproductive organs, are shared.
They were born in 1990 with a partly-formed third arm which was removed when they were 12 and had surgery to correct spine curvature and help their breathing.
But they grew up so strong that parents Patty, now 46, a nurse, and Mike, 47, a carpenter, never considered having them separated, as they would each have had just one arm and leg and been confined to wheelchairs.
Patty says: “From the first time we saw them we thought they were beautiful.
“I kissed Abigail and then Brittany and gave them both a hug.
“It’s been like that ever since – two kisses and a hug for the most beautiful children in the world.”
Although Brittany can’t feel anything on the right of her body and Abby nothing on the left, they stunned everyone with the instinctive way they co-ordinated their limbs as they learned to clap, crawl, walk, run… and scratch each other’s itches.
Their parents, brother Dakota, 20, and sister Morgan, 18, encourage them to be as individual as possible.
Growing up in a town of just 300 people they were treated no differently from anyone else.
But outside this close-knit community strangers would stare, take pictures and make comments.
“When children ask if they have two heads, they say they don’t. They each have their own.
“That’s what we have encouraged them to do, to develop their own individuality as much as possible, ” says Patty.
Despite their two different personalities they rarely fall out.
They talked about separation only once as small children, when Brittany was confined to bed with pneumonia.
Abby got restless and wished she could get away.
But when Brittany cried Abby reassured her they would never be parted and offered to take her medicine for her.
Now the twins are putting themselves in the public eye there are bound to be more questions.
Three years ago, unconfirmed reports claimed Brittany was engaged.
If they have started dating, what if one twins hates the other’s lover?
The TV show might provide some answers. But for now the twins seem as happy as ever.
Abby says: “The best thing about being conjoined twins is there’s always someone there to talk to.”
Brittany nods in agreement. “And you are never alone,” she smiles.