"We were so picky with what songs we put on this record," Colton, 26, tells PEOPLE. "And we said a little prayer before every session with the musicians, just praying that it goes well. You get one shot at this."
Of course, it helps to have friends in the biz like their mentor from The Voice, Blake Shelton, whose advice they took to heart while working on the project.
"From day one Blake definitely guided us. I know the cameras have stopped rolling, but he's still mentoring, still coaching, as a friend," says Colton. "He just told us, 'Man, you're the ones that got to sing these songs for the next 20 years if it's a hit. Be sure that they're songs you want to sing and that it's something you want to say.'"
So will Shelton be collaborating on the project? "The biggest question we get is, 'Did you talk Blake into singing on the album?'" says Zach, 29. "And we definitely talked about it and he was on board, but I think we're going to save that for when we find the right song."
In the meantime, the brothers say making their first album, due Oct. 14, is an experience they will never forget – both the good and the bad.
"I've never eaten so many sub sandwiches!" says Colton. "You would think, 'Oh they're living the high life,' but no, we were eating sub sandwiches every day we were in the studio, just to save time. You get up, put your sweatpants on and you know you're going to eat a sub sandwich – definitely not glamorous."
But their most memorable moment in the studio was an emotional family affair.
"The next day, we went into the studio and they got to come. Our dad has always had some kind of recording equipment in the house since we were little, whether it was a 4-track recorder, or as the years went on we kept advancing our home studio. But for him just to sit behind the big console and watch us do what we do, it was a pretty cool experience. They got choked up and were real proud. It meant a lot to them and it meant a lot to us."
"Of course you still have our mom in there trying to correct us and tell us how to sing," adds Zach. "It gave us a little taste of home."