"What's getting us through this now is believing in each other and the love that we have," Kim Kirzow Spratt tells PEOPLE

Credit: Courtesy Kim Kirzow Spratt

It was supposed to be a romantic “babymoon” – one last trip overseas alone as a couple before the arrival of their boy and girl twins.

Now Kim Kirzow Spratt and her husband, Fred Spratt, of Jackson, New Jersey, are grounded in Portugal after the loss of one baby, while their other preemie is fighting for her life in a neonatal intensive care unit.

“We’re having to dig deep, keep our spirits up and find a strength we never knew existed,” Kim, 31, tells PEOPLE from Lisbon, where she and Fred have been shuttling between Maternidade Dr. Alfredo da Costa hospital’s NICU and a small apartment for almost six weeks. “We realize we’ve been dealt an unimaginable situation. It’s the hardest thing as a couple that we’ve ever had to endure.”

The Spratts were one week into their dream vacation on Mother’s Day, May 10, when Kim, a physical therapist who was six months pregnant but had been cleared by her doctor for an overseas journey to Spain and Portugal, suddenly felt sick and started cramping after a sunset dinner cruise in Lisbon.

Kim was admitted to the hospital just after midnight, and it was discovered that she was in the late stages of labor – 13 weeks early.

“Everyone was speaking Portuguese in the delivery room, and I didn’t know what was going on,” she says. “I’ve never felt so alone and frightened.” Fred Spratt, 36, a lock salesman, was not allowed to join his wife during the babies’ emergency deliveries.

“They made him wait in the lobby,” Kim says. “I didn’t have that feeling of smiles and happiness with my husband at my side, holding my hand.”

Hudson Charles Spratt was born first, weighing 1 lb., 12 oz., followed by his sister, Hayden Grace, one minute later at 1 lb., 7 oz. The babies were whisked away to intensive care, so unstable that they couldn’t be touched. Two weeks later, on May 24, the Spratts received an early morning call at their apartment with the news that Hudson had died. They had never even held him.

“I think of his face that looked just like his daddy’s, and when he held my finger,” Kim tells PEOPLE, “and it brings tears, but also smiles. He will always be our son, our hero and our champion.”

Hayden still weighs about the same and is holding on, she says, but will likely be in the hospital for weeks or even months. Once she is healthy enough to leave intensive care, the Spratts will still have to remain in Lisbon until doctors clear their daughter for a chartered medical flight back to the United States.

“The last thing we want is for Hayden to fight this long fight, then have her immune system compromised getting home,” says Kim, who spends all day at the hospital with her daughter and Fred and is now able to hold her for brief periods and bathe her.

To help the Spratts cover their expenses, Vanessa Adams, Kim’s best friend, started a GoFundMe page, which has brought in almost $40,000 so far.

“As a new mom myself, there’s pretty much nothing I can imagine as horrific as watching your children suffer and one of them die,” says Adams, 31, a wedding photographer from Freehold, New Jersey.

“Kim and Fred are fighting hard, hand-in-hand, for their new baby girl,” she tells PEOPLE. “The money we’ve raised has helped with hospital bills but also has helped alleviate the loss of income they’ve experienced while they’re away. Our ultimate goal now is to figure out a way to help them find a way home with Hayden much sooner.”

Kim says that she and Fred, who met online through Match.com and married in February 2014, were ecstatic when they learned they were expecting twins, breaking the news to their families at Christmas. “Then just before Easter, we found out we were having a boy and a girl,” she says. “We were over the moon that we’d get the best of both worlds.”

Realizing they wouldn’t have another chance to get away alone for a while, they booked a trip, leaving plenty of time before Kim’s Aug. 25 due date.

“What’s getting us through this now is believing in each other and the love that we have,” Kim says. “We look forward to getting home, living a normal life again and introducing Hayden to our dog, Bauer, and our friends and family. We have yet to really feel that overwhelming feeling of happiness – that, ‘Hey, we are parents.’ That’s what our eyes are set on. We have gotten very good at being patient and waiting, knowing every day that every moment is a big moment.”