Family members say love story of Dalton, 25, and Katie Prager, 26, endures despite young lives lost to cystic fibrosis

Credit: Prager Family

In their final days, real-life Fault in Our Stars couple Katie and Dalton Prager put on the best face they could for each other, sending love and encouragement via Skype across the miles that separated them as each withered from the cystic fibrosis disease that claimed their lives within five days of each other.

And when Dalton, 25, unexpectedly died first last Saturday, his family found comfort thinking that he was paving the way for Katie, 26, his wife of five years, to join him yesterday.

“He’s a gentleman,” Dalton’s dad Dave Prager tells PEOPLE. “Everybody’s in the belief that Dalton was there to open heaven’s gate for her.”

Katie’s death Thursday came after she told her family she did not want to endure any more hospital stays, and had chosen to spend her last weeks at the couple’s Kentucky home in hospice care. Dalton, meanwhile, wrestled his own illness under the watch of his family in Missouri, where he wound up back in the hospital on the very day he’d planned to travel to lend Katie his support and see her one last time.

Both were born with the genetic cystic fibrosis disease that restricts and worsens the ability to breathe over time, with a current average life expectancy of about 40 years old. Although each received a lung transplant – Dalton in November 2014, and Katie in July 2015 – neither fully recovered.

The time they spent together since their surgeries was measured not in days, but in hours. But the families of both say the couple’s love story endured.

Dalton – who was most recently on a ventilator and often sedated in his hospital room – was able to connect via Skype with Katie last Thursday. “You could tell he was struggling in his own pain,” says Dave.

But the sight of his bride transformed him. “When he saw Katie, his eyes just lit up,” Dalton’s dad says. “He wanted everything to look positive for her. He pulls that off quite frequently for her.”

Katie, too, put her fighting spirit on display. “Katie was just always positive reinforcement for him,” says Dave. “That was one of their deals with each other: ‘It’s going to be okay, it’s going to be okay.'”

But the next night, when the family tried to unite Dalton and Katie again, “he wasn’t coherent enough to communicate,” Dave says. “That was tough.”

Dalton died the next afternoon, on a day when Katie gathered with her family for an early Christmas because her doctor had told her she likely would not live to see the holiday. Only a week earlier, Dalton’s brother, Nathan, and Dave had driven the seven hours from St. Louis to Flemingsburg, Kentucky, on Dalton’s behalf to see Katie, stopping at the Dairy Queen there so they could deliver her favorite strawberry cheesecake Blizzard “with extra cheesecake chunks.” Their trip was cut short by a call from Dalton’s mom, saying he’d made a turn for the worse and they’d better come back to be by his side.

Katie was able to join in Dalton’s visitation on Tuesday by Skype. The two had last seen each other in person in July, for a few minutes in Katie’s hospital room on their fifth wedding anniversary. Dave had driven with his son to pull off the visit. “He was not in good shape then,” Dalton’s dad says.

“I was a little scared. Seeing Dalton sitting on the hospital bed next to Katie – I hadn’t seen Katie for a while, and she was very thin, very frail – it almost made Dalton look normal size. I don’t think Dalton looked at it that way. He was just glad to be there with her,” Dave says.

Talking with Katie after Dalton died, “you could tell she was heartbroken,” says Dave. “I don’t know if that was the final straw for her.”

Until then, Katie had shared updates on the couple’s Facebook page, chronicling Dalton’s progress as he tried to get well enough to see her. Before her daughter died, Katie’s mom Debbie Donovan told PEOPLE: “She has just told me that she would just like to have a conversation with him and just hug him and kiss him and let him know that she cares for him. Even if it’s just for five minutes, she just wanted to be able to say that to him.”

When the families once more tried to connect Katie via Skype into Dalton’s memorial service, “we got a reply from her mother that Katie was not well enough to participate,” says Dave. “That was just prior to her passing early the next morning.”

In the social media tributes that sprouted to celebrate each of the young lives lost, Dave finds joy in rediscovering “they’re just two goofballs … just kind of hot-dogging for the camera.”

Dalton, he says, had feared he might never experience romance at all. “He didn’t think he’d ever find somebody that would accept him,” he says. Dalton also fretted that he’d be forgotten, never mind that he achieved his goals of surviving past his teen years, earning diplomas from high school and culinary school, supporting himself by working, building a relationship, buying a home and traveling. “He darn-near accomplished everything he wanted to,” says his dad.

And his family’s work with cystic fibrosis isn’t over. Dalton has two cousins with the disease. “They’re fighting the same battle,” says Dave. “If this is his legacy, to get the word out about cystic fibrosis, I think he would love it.”

At Dalton’s funeral, his family concluded the service by playing Dalton’s favorite song, the Lynyrd Skynyrd anthem “Simple Man.” In their mind’s eye, Dalton was the upfront lead singer who finished the number, threw down the microphone, then walked off the stage saying the words, “Peace out.” Says his dad, “That’s the way we envisioned it.”

But they also see Dalton greeting Katie, with her strong faith, into the hereafter.

“Maybe that was his dying wish, to be there for her,” Dave says. “We just envision him opening the door.”