Parents of 3 in 'Race Against Time' After Their 2 Daughters Are Diagnosed with Fatal Brain Disease

"Every single day that goes by, we are losing a little bit more of them," Kyle Harrison says of his two daughters, Kinley and Kennedy, who have GM1 gangliosidosis

Kinley, Kennedy and Kieran Harrison. Photo: Courtesy Harrison Family

The parents of three young girls are doing whatever they can to improve the quality of life for their two daughters after both were diagnosed with a fatal and incurable brain disease.

Kyle and Kylie Harrison were in complete bliss on June 4 after welcoming their third daughter, Kieran, to the world.

But just one day later, the Colorado couple's world was flipped upside down when they learned their two older daughters — Kinley, 7, and Kennedy, 4 — had been diagnosed with GM1 gangliosidosis.

The rare, genetic disorder progressively destroys nerve cells in the brain and spinal cord, and will likely kill the girls by early adulthood due to the fact there is currently no cure, according to the U.S. National Library of Medicine.

"When we found out, we were a complete disaster," Kylie, 35, tells PEOPLE. "It was very scary."

"We went from a super high the night before to getting hit twice," Kyle, 34, says. "They have a chance of surviving into their teens and early 20s, but it's only a couple of years away that one or both of them will be confined to a wheelchair or on a feeding tube."

"At some point, they won't recognize mom and dad when we walk into the room, they won't be able to talk to us, won't be able to say 'I love you' anymore," he adds. "That reality is right around the corner for us, unfortunately."

Kinley Harrison. Courtesy Harrison Family

As their time with their two daughters becomes limited, Kyle and Kylie have set out to raise $2 million dollars on a GoFundMe page to get the girls through a one-year clinical trial, while also hoping to generate awareness about GM1.

"There's no playbook for GM1 and what to do next. It was, 'Here's the diagnosis and there is not a whole lot that we can do about it," Kyle explains. "We refused. We don't accept that. We believe strongly there is something we can do."

The couple says they first noticed signs of the genetic disorder when Kinley was 2 years old and started to exhibit speech and other developmental delays.

At the time, doctors struggled to determine why she was having so many learning problems and issues with spatial awareness and balance, assuming it was due to her need for glasses and ear tubes, but Kyle and Kylie remained firm in their desire to find concrete answers and insisted on more testing.

Within the last six months, Kennedy also started showing similar signs, so the parents had genetic testing done. The results confirmed both girls had GM1, and Kyle and Kylie were both carriers, which brought on even more worries for the couple.

"Your mind is going a million miles an hour and then you stop for a second and think, 'Our two kids have a fatal genetic condition and we have this third baby that just got here who might also have it,' " Kyle recalls.

Kennedy Harrison. Courtesy Harrison Family

Luckily, testing determined that their daughter Kieran is not a carrier of the disease, but doctors maintained their stance that Kinley and Kennedy's days were numbered and there was not much that could be done.

"The thing with rare diseases is they are not on everybody's radar so they don't get a lot of attention or funding, and families like ours are left without a whole lot of options," Kyle explains. "We are in a complete race against time. Every single day that goes by, we are losing a little bit more of them."

"To be told there is literally not a single treatment for this or anything that they could do is ridiculous," Kylie shares. "We have to do everything we can to advocate for them so we can hopefully give them a quality of life that they deserve... We are not going to stop fighting for them."

Currently, Kinley and Kennedy are verbal, can easily move around, and enjoy playing on the playground — all behaviors that Kyle says are non-typical of children with GM1 — but the father of three heartbreakingly notes those abilities won't last forever.

"The reality is without the awareness, without the funding, this disease is going to take their lives. There is no question about it," Kyle says. "It's going to rob them of life... You start thinking about all the things that they're going to miss out on and what the reality for our family is going to be over the next several years."

The Harrison family. Courtesy Harrison Family

"We were getting ready for family pictures a few weeks ago and Kylie was braiding Kennedy's hair, and she started breaking down and... thinking about how she probably was not going to be braiding her hair for prom," he continues. "There's going to come a day where I wish they could talk back to me and have an attitude with me."

Still, even with an uncertain future, Kylie and Kyle do their best to maintain a positive outlook for their girls – and for themselves.

"It's an impossible task but one that we have to do," Kyle says. "We've been telling ourselves that there's a reason that they were sent to us and why they chose us to be their mom and dad. We are going to give them the time of their life while we can."

"You've got to live in the moment and you can't go down those rabbit holes because you'll miss out on what's happening in front of you," adds Kylie.

As they embrace those moments with their daughters, Kyle and Kylie are holding onto hope that their efforts will benefit the girls in treatment, as well as provide more research and funding for other families in similar situations.

"Even if it's too late for Kinley and Kennedy — and we pray that it is not — Kylie and I want to make sure that someone else in our position several years down the road doesn't have to feel so isolated and feel so hopeless like we feel right now," Kyle says.

"We're fighting for Kinley and Kennedy because right now, they can't really fight for themselves," he adds. "We have a chance. It may be a small one, but we've got one."

Those interested in donating to the Harrison family's GoFundMe can do so here.