"We always felt like women," Chloe, 20, told InsideEdition.com.
Despite growing up in a supportive environment, both Jamie and Chloe agreed that understanding who they were separately was lonely — until they discovered they were going through the same thing.
"It's not like I didn't want to tell any of my family members," Jamie, 23, said. "I didn't fully know, and I didn't want to tell people until I fully knew what I wanted to do."
It all started when Jamie was 3, and Chloe was still in the womb.
"My mom was convinced Chloe was going to be born a girl," Jamie told InsideEdition.com. "I got it in my head that I was going to have a sister."
She was so convinced, that she even helped her mom choose the name 'Chloe' for her younger sister.
"She came out as 'Daniel', this little boy 'Daniel,'" Jamie said, when her mom finally gave birth to a boy instead of a girl as they had expected. "I'm there going, 'Where's my sister?'"
She speculated that their relationship would have been different had Chloe been born a girl, but "that's not the way life went. That's not our journey — this is our journey now, and I feel like we've become so much closer because of it."
Despite being assigned male at birth, Chloe said that they have both suspected they were transgender throughout their childhood.
"We were putting tops on our heads to make it look like (long) hair, and tops on our bottoms to make it look like skirts -- anything we could find to make us look feminine, we would do," Jamie said. When they played together as children, they even called each other by their female names.
Slowly, Jamie said they began growing apart. By the time she became a teenager, and her sister was entering her preteen years, they no longer had much in common.
"I was going through my own thing, and she was going through her own thing," she said. "We kind of drifted apart."
By 16, Jamie — who had come out as gay two years prior — began performing in drag.
"I was always much happier in drag than out of drag," she said. "It was like going back into my childhood, and experiencing being that feminine again. I just felt so comfortable."
Through drag, Jamie said she began exploring her own gender identity. Even though their mom, who is a lesbian, has asked many times whether Jamie thought she was transgender, it was not until she began speaking with her transgender friends more did she begin questioning it.
Chloe told InsideEdition.com that her realization was last summer during debs, the Irish equivalent of an American prom.
She said she wore her bleach blonde hair long and sported a full face of make-up.
"I remember Jamie turned to me and said, 'You look like a woman. You look so feminine and beautiful,'" Chloe, who identified as gender fluid at the time, said.
Chloe was then asked if she thought she might have been transgender. "At the time, I was so mentally drained. I didn't know in my head what I was going to do, so I kind of said, 'I'm not sure.'"
To which Jamie replied, "Me too. I'm kind of confused about it."
"After that, we started the conversation of, 'Are we going to transition?'" Chloe said.
Though the process was once lonely, with Jamie living in Dublin and Chloe living in Cork, Jamie said that helping each other understand their transition has helped them grow closer together.
"I would not be able to be on this journey without her," Jamie said about her loving sister. "It's so amazing to have that support."
Their next battle is coming to terms with the gender reassignment surgery.
Jamie said her hesitation was due to her fear of anesthesia and hospitals.
Chloe however, said, "to be honest, I'd do it tomorrow if that were an option," although she admitted she still has a ways to go in mentally transitioning before she is ready for the physical procedure.