'The Most Miraculous Thing I've Ever Seen': Why 'Squeamish' Thomas Rhett Is Glad He Watched Ada James' Delivery

"I got a little glimpse from this mirror that was set up and I was like, 'Well, I'm invested now,' " Thomas Rhett tells PEOPLE of his daughter's birth

Cuddling together on a bed, their newborn between them and their 21-month-old in constant movement — over, around and on top of them — Thomas Rhett and Lauren Akins are marveling at their long journey toward becoming a family of four.

The country star and his wife had been shuttling back and forth to Uganda for a year trying to adopt Willa Gray before finally bringing the toddler home to Nashville, Tennessee, in May

“I didn’t think she would ever come home,” Lauren tells PEOPLE in this week’s issue, posing with her family for a sweet photo series shot by Julie Paisley. “It was so exhausting, so defeating. Emotionally, it would wreck me sometimes.”

And baby No. 2, Ada James, didn’t make it much easier on her mama. Sick for the first 20 weeks of her pregnancy, Lauren struggled through a marathon 36-hour-plus labor session before Ada was born on Aug. 12. “I feel like I went through two separate births,” she says. “And they were not easy pregnancies, either one!”

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Julie Paisley Photography

At her side for both was Thomas Rhett — much to Lauren’s surprise. “It shocked me how involved he was with Ada because ever since I’ve known him in middle school, he has been the most dramatic, can’t-deal-with-anything-too-intense person,” she says. “He’s squeamish and he will tap out at the drop of a hat, but through those first 28 hours, he did not leave my side.”

Lauren had hoped she would go into labor on her own, but as her Aug. 8 due date passed and time grew short before Thomas Rhett would have to leave town for a show, so they decided to induce. “It was more important for him to be home for a little bit than to wait for my body to do it all on its own,” Lauren says.

She was, however, committed to a natural birth — a choice Thomas Rhett says he couldn’t understand. “I don’t do pain,” he says. “If there is a drug to be taken to not make pain happen, I’m on it.”

Julie Paisley Photography

RELATED VIDEO: Thomas Rhett and Wife Lauren Akins Welcome Second Daughter

The singer and Lauren’s mother spent hours in the hospital, massaging and pushing on Lauren’s pressure points as she endured contractions. “I’m like, ‘You really don’t want drugs right now? If I were you, I would have taken drugs right when I got here,’ ” he says.

“She was so strong-willed, but there came a point where we weren’t getting anywhere and it was so painful that she finally did.” It was, he jokes, “the best moment of my life!”

• Watch the full episode of PEOPLE Features: Thomas Rhett – Meet My Baby Girls, available now on the PEOPLE/Entertainment Weekly Network (PEN). Go to people.com/PEN or download the PEN app on your favorite mobile or connected TV device.

When things finally started moving, Thomas Rhett firmly planted himself at the head, rather than the tail, end of the operation. “I promised myself I wasn’t going to watch,” he explains. “And then I got a little glimpse from this mirror that was set up and I was like, ‘Well, I’m invested now.’ ”

“When I saw Ada come into the world, it was literally the most miraculous thing I’ve ever seen,” he recalls.

Julie Paisley Photography

RELATED GALLERY: The Fab Four! A Peek Inside Thomas Rhett and Lauren Akins’ Family Life

Willa Gray, however, wasn’t nearly as impressed with her first glimpse of her baby sister. In the weeks leading up to the birth, she had been fascinated with Lauren’s belly, continually repeating “Ada? Ada?”

But when she saw the real thing, “I think it wrecked her when she realized it was a human instead of a baby doll,” Lauren says.

FROM PEN: How Today‘s Savannah Guthrie Copes With a Toddler, a Newborn AND 3 a.m. Wake-Up Calls!

During the sisters’ first meeting in the hospital, Willa refused to say Ada’s name. In a video Lauren posted of the moment, she looks a little shell-shocked, but did reach for Ada’s hand and, with a little encouragement, gave her a quick kiss.

“It was so sweet,” Lauren says. “Willa loves to hold my hand, and she started rubbing Ada’s hand like I do with her.”

Back at home, it’s been a little less picture-perfect, Lauren admits. Though Willa is “finally coming around to the baby,” it hasn’t been easy. “She has to take a back seat with me because Ada just needs me so much more. It’s hard to explain to a 21-month-old that ‘Mommy can’t hold you,’ ” Lauren says.

The toddler is, however, intrigued by Ada’s crib (“She wants to lie down and take naps with Ada,” says Lauren) and, adds the mom of two, “I think she’s growing to love her more and more.”

Julie Paisley Photography

As for Ada James, she seems to embody her given moniker. “Ada means happy,” says Lauren, who researched baby-name meanings before she came up with the perfect fits for both her girls (the newborn’s middle name is in honor of four different family members).

“It was beautiful, and I thought, ‘Well, she’s the happiest little surprise we’ve ever had,’ ” Lauren adds.

For more on Thomas Rhett and Lauren Akins’ new life as parents of two, pick up the latest issue of PEOPLE, on newsstands Friday.