At just three years old, Aly McGarrity was a tomboy who enjoyed playing football with the boys, while older sibling Russie, then 5, preferred playing dress up with the girls.
Mrs McGarrity said her school struggled to understand her struggle and even threatened to expel her after she ran into the girl's toilets.
For Russie, now known as Rai, the next few years were hard, her mother Beth told Good Housekeeping.
At high school, she was bullied by other students but refused to bow to pressure to conform and adopted an androgynous look.
'I would rather be hated for who I am than loved for who I am not,' she told her parents.
Mrs McGarrity, from Connecticut, says she always knew her children were a little different.
'I did not choose this for myself,' she had told her mom. 'I wish there was a way that I could not be this way.'
While the family were concerned with Rai, unbeknownst to anyone, Aly was also struggling with gender.
Aly, now known as Gavin, had always been a bit of a tomboy but deep down he knew there was more to it.
After researching transgender on the internet, he realized that he had been born the wrong sex. He wanted to be a boy.
And it was Gavin who took the brave step to come out to his parents first.
Just a few days before his 15th birthday, he broke the news to Rai that he was transgender. Then, they broke the news to their mom.
'I've figured out what's going on with me,' Gavin told her. 'I know that I'm transgender. I've always wanted to be a boy. I never told you this, but when I was little, I would go to sleep and wish that I'd wake up a boy.
'Every time we did the wishbone at Thanksgiving and I won, I would wish that I was a boy.'
A month later, Rai confessed that she too was transgender and both siblings, after receiving counselling, have decided to go ahead with gender reassignment surgery.
Gavin, now 17, said that it had been his parents' unwavering support and unconditional support that had allowed him and Rai, now 20, to become the people they wanted to be.
'Even in the years when (mum) didn't know what was going on, before I came out, I knew that all she cared about, at the end of the day, was me and Rai being happy,' he said.
Father Russ said he had always hoped to have a boy and a girl.
'As it so happened, we did have one of each — just in a different order than we originally thought,' he said.
Gavin is now due to undergo surgery to remove his breasts while Rai has already had a painful facial surgery to appear more feminine.
Rai, who has a boyfriend, also video blogs about her life as a transgender woman and has more than 6.5million views.Mrs McGarrity said: 'People ask me what I've lost, but I don't feel that I've lost anything. I have my son and daughter the way they should be'