Gwen Stefani's 3 Sons 'Will Have a Large Part' in Her Wedding to Blake Shelton, Says Source

Blake Shelton and Gwen Stefani can't imagine saying "I Do" without three very important people by their sides: her kids!

A friend in the couple's circle tells PEOPLE in this week's cover story, on newsstands Friday, that the No Doubt rocker's sons Kingston, 14, Zuma, 12, and Apollo, 6, "will have a large part" in her upcoming wedding to the country star.

"Gwen's sons are just really solid, sweet kids, and they're so excited for Blake and Gwen to get married," says the friend. "They can't wait to stand by their sides."

Shelton, 44, and Stefani, 51 — who announced their engagement on Instagram Oct. 27 — first struck up a friendship in 2014 while working together on the coaches' panel of The Voice’s seventh season. Both married at the time, it wasn’t until a year later that their relationship turned romantic while they leaned on one another during their respective divorces. (Stefani announced her split from Bush frontman Gavin Rossdale in 2015 after 20 years together just weeks after Shelton and his ex-wife, country singer Miranda Lambert, finalized their divorce following four years of marriage.)

"At first they were bonding over their splits and finding light in one another, but they quickly realized they have so much more in common than just going through heartbreak," says the friend. "They're both incredibly close to their families and their lives are rooted deeply in their faith. He just fit so seamlessly into her life, and vice versa."

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As Shelton’s bond with Stefani blossomed over the years, so did his relationship with her three sons.

"From the beginning, Gwen made it clear to Blake that her boys were No. 1 in her life, and Blake always respected this," says a source close to Stefani. Adds the friend: "He never wanted to overstep and made sure everyone was comfortable with his role in her sons’ lives."

As Shelton slowly introduced Kingston, Zuma and Apollo to the laidback lifestyle on his Tishomingo, Oklahoma, ranch, where they often spend time fishing and camping on holidays and school breaks, Stefani fell deeper in love.

"Gwen always gushed about how amazing Blake is with the boys," says the Stefani source. "She feels so lucky that he helps her raise them. His love and guidance is something that Gwen is beyond grateful for."

RELATED VIDEO: Gwen Stefani Shows Off Her Engagement Ring from Blake Shelton During The Voice Live Shows

When Shelton was planning his proposal, he knew he wanted Stefani's boys to be there.

"The only thing I had planned was that I knew I wanted to do it in Oklahoma while all her kids were there [and our siblings],” Shelton told radio host Bobby Bones on Dec. 14. "I didn't want to take her away or do something private away from the kids. I felt like it was important for the kids to be a part of that moment, so that's what I did."

After getting permission several weeks earlier from Stefani’s dad Dennis, as well as her sons, Shelton bought the engagement ring — which WP Diamonds CEO Andrew Brown estimates to be seven carats and worth at least $250,000 — and kept it hidden in his truck.

"I had the ring in the compartment on my door of my truck for about a week," Shelton said. "[When I was] digging in there looking for a flashlight or change, I kept thinking, 'Man, somebody's gonna hit the jackpot whenever I drop this thing out of my truck.'"

RELATED: Blake Shelton Hid Gwen Stefani's Ring in His Truck for Weeks: 'Thank God I Didn't Lose It'

Luckily, Shelton didn’t lose the ring, and the proposal turned out even better than he could have imagined.

"Gwen was amazed and absolutely not aware the proposal was happening," says an industry source. "It was a shining point in her life."

Sources expect the couple's nuptials to take place in a chapel Shelton built for Stefani on his ranch — the singers gave fans a peek at the special place in their engagement announcement — and for the wedding ceremony to be intimate and emotional.

"It will be smaller with family and only close friends," says the industry source. "They aren't rushing it now but do want to marry soon."

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As they continue to split their time in quarantine between Oklahoma and California, Stefani and her sons are thankful for the respite that Shelton's ranch offers.

"Blake's life in Oklahoma is very different from their L.A. life," says the Stefani source. "They have a lot of freedom there and can do outdoor activities. It's been such a perfect escape during COVID."

It’s also provided a burst of creativity for both Stefani and Shelton, whose duets "Nobody But You" and "Happy Anywhere" both went No. 1 after their releases in April and December, respectively. Then on Dec. 15, Stefani earned her first Voice victory with contestant Carter Rubin one week after seeing her new single "Let Me Reintroduce Myself," reach the top of the iTunes chart following its debut.

"It's just such a different chapter," Stefani — who hadn't released solo, non-holiday music in four years — told Apple Music's Zane Lowe on Dec. 7th. "Life's gotten so good."

And now with a wedding on the horizon, 2021 is looking even brighter.

"Gwen didn't think an engagement would change her and Blake's relationship because it felt like they were already married, but it has sparked even more happiness," says the Stefani source. "The wedding has given her something amazing to look forward to in the new year."

For more on Gwen Stefani and Blake Shelton's wedding plans, pick up the latest issue of PEOPLE, on newsstands Friday.