Kevin Jonas Sr. and Wife Denise, Married for 39 Years, Share Rare Family Photos as They Sing on New Holiday Album (Exclusive)

"They're so excited about it, and that makes my heart," the Kevin — who's dad to the Jonas Brothers — tells PEOPLE exclusively about his debut Christmas EP

The Jonas family take the holidays very seriously, and now Papa Jonas is hoping to create more festive memories for his loved ones with his debut Christmas EP.

Kevin Jonas Sr., who's dad to music superstars the Jonas Brothers, released a new batch of tunes titled Ready Set Glow – A Holiday Collection with his five granddaughters in mind.

"The granddaughters love it, and that makes us very happy," he exclusively tells PEOPLE about the project, which saw the music manager and businessman collaborate with wife Denise. "That was the reason for the Christmas project right there."

The seven-track project was initially intended as a surprise gift for Denise after she spent nearly 35 years trying to convince him to craft a Christmas album. "We had a period of time where we were managing the guys, our sons, and then there was a break," he explains about his decision to finally make the EP happen.

"We both had some medical issues to deal with, and we restarted our entertainment company about four years ago. We've hired some folks, and it was that group of people that said, 'You really should do this.' And I said, 'Yeah, my wife, she's been saying that for many years.' They were like, 'Let's surprise her.' So we started working on it as a surprise."

However, the surprise was spoiled during a car ride phone call, which actually presented an exciting opportunity. "He did a conference call with this person on the phone, and she just spilled it all out," Denise recalls, with Kevin adding, "The surprise left, but it gave me an opportunity to ask Denise to join me on one of the songs, which made up for it."

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The couple, who recently celebrated their 39th wedding anniversary, collaborated on the EP's title track, and despite Denise's initial hesitation, her husband's assurance gave her the confidence to lend her singing voice.

"I resisted it," she admits. "I just didn't know how I could compare to his voice and his ability, but I did it, and I'm happy with how it came out."

"It's wonderful," Kevin exclaims. "My feeling is it's the best song on the record and the last time we recorded something together was probably 40 years ago. She has a beautiful voice."

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Denise's rare musical appearance surprised no one more than Nick and Priyanka Chopra Jonas' 2-year-old granddaughter, Malti. "Every time that part of the song comes on, she just leans forward and just stares," laughs Kevin, with Denise adding, "I think she's totally confused, but she sings every word."

"We had to play it for her 11 times straight. She loved it," Kevin notes.

The album is a Jonas family affair, with the couple's youngest son Franklin providing backing vocals on the track "ChrisMess" and "Joy to the World (A Christmas Prayer)" being a song Kevin wrote with his son Nick when he was a child.

The couple didn't tell their kids they were working on the project, and were nervous to play them with the final product.

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"They're so good at everything they do and there's always a little bit like, 'Okay, are you going to think dad's hokey'," Denise admits. "But they were just so kind and so embracing of it."

"The reaction was so positive that we played it slowly, one song at a time for each one — and carefully, because it really wasn't intended to be anything but a gift," Kevin says. "Just so supportive, but for me, watching my granddaughters dance around to the song... that makes my heart."

The pair call the holidays a "celebratory" time for their family packed with traditions new and old. They recall always taking out Christmas ornaments while decorating their family tree, explaining the origin story of each one. Denise remembers an annual event that left their son Joe hospitalized when he was a kid.

"We would do Christmas Eve fish dinner, and I would purchase shrimp that had to be shelled and cooked," Denise says. "I did that on purpose, so they would all sit around the table with me in the kitchen, taking the shells off while I'm doing other things. It was always fun and laughter, but when Joe was about eight, his hands started getting red and swelling up, and then it moved to his face. Kevin took Joe to the hospital, where he had to stay for a couple hours because he developed this shellfish allergy."

It's memories like those that keep the Jonases laughing, noting that their expanding family and busy schedules have made it difficult to all be together for the holidays in recent years. But even if they can't be together on Dec. 25, they always find a day to do a "Jonas Family Christmas."

"My wife always makes Christmas a memory," Kevin gushes about his wife. "If we were at a hotel in New York, she would go find a small Christmas tree and put it on the table and made sure the gifts were there and the food that was special for our family was always available."

Now they feel an immense sense of pride seeing their grown sons share the joyous season with their own children. "They love those girls and they all take time to make special memories," says Kevin, with Denise exclaiming, "watching them be parents at Christmas and watching them do things that we always did, we notice it and it just gives you a warm feeling inside!"

Denise also points out how happy she is to see her daughters-in-law get involved each year, regularly asking for family holiday recipes for meals and cookies to make with their own kids.

"Everybody says we did a great job raising those boys, and we had a part in it, but they've chosen to be these really wonderful adults and people, so it's not all on us," she says. "They are amazing."

"I'm learning from them," Kevin adds. "We've thanked our kids for reminding us to celebrate the moments and for helping us continue to evolve. That's a gift back to us."