Helen Morfitt, 56, started life as Leslie, and is due to marry Felix Laws, 46, formerly Katy, in September.
Between them, the couple has already been married four times, and Helen has eight children and Felix two from their previous relationships.
They will officially change their gender on their birth certificates, allowing them to get married, with a date set for 13 September, the date both had their sex change operations, albeit seven years apart.
Helen told the Daily Mirror: "We've been through a lot over the years and had tough times transitioning from one sex to another, but we've now found each other and that's all that matters.
"I've been married three times before but this time I know it's for real because I know I'm the right sex this time."
Felix added: "We're just like any other couple - including in the bedroom. Neither of us has any complaints on that score."
The couple met in 2008, when Felix visited a doctor about the possibility of having a sex change operation. The doctor referred him to a transgender support group run by Helen.
"As a child my friends were playing with dolls and prams but I wanted to climb trees, play football and get muddy," said Felix.
"Even sitting down to go to the toilet felt wrong. But it was the 1970s and you didn't have those kind of thoughts back then."
He got married as Katy at 21 and soon had two children.
"After I exchanged vows with my husband and went up to our room I knew I'd made the biggest mistake of my life.
"Just because I was transgender didn't mean I didn't want what everyone else had - a loving family.
"When I held my children in my arms for the first time I felt like any other mother would about their baby."
After 13 years, Felix left the marriage and the children.
"I didn't have a choice. The urge to become a man was growing stronger.
"My husband was given custody of the children and it broke my heart but I couldn't keep playing happy families," he said.
Helen married three times as Leslie.
She said: "My wives had wanted children and I did too. In some ways I was trying to prove my masculinity, trying to deny who I really was - a woman in a man's body.
"I loved my wives, in fact I'm still friends with two of them. But I couldn't love them in the right way. I was trying to repress my real feelings and coped by cross dressing in secret."
Both said that one of the most difficult parts of the process was telling their families of their decision to change sex.
"I told my two youngest, who were only five and six, that I was very poorly and the only way I could get better was to become a girl. They accepted it easily," said Helen.
"The six-year-old said it would be a bit silly to call me Daddy and started calling me Helen.
"My two girls and four other boys came round to the idea slowly and I regularly see most of them now."
Felix recalls telling his 16-year-old son: "He asked me if I was a tomboy. He told me he'd watched documentaries about transpeople.
"He then asked me if that's the way I felt. I was gobsmacked that he was so intuitive. We've had an incredible relationship ever since."
For the Gretna Green ceremony, Felix will be swapping the flowing white dress of his first marriage for a kilt, and Helen will wear the black gothic dress she dreamt of when younger.