Hmmm... I wonder if he's not a little worried about what the band is snowballing into. After all, besides the booked gigs, you're looking at a soundtrack deal, a sponsorship (which carries with it WAY more gigs- I'd be shocked if it was much less than 50 a year)...
He signed on because he liked to play music but it still lives in "hobby-ville" for him. Nothing inherently wrong with that. You've gotten a taste of success and now wonder where that might eventually lead. You're worried that losing momentum here might result in 40 years of wondering what might have been.
From what you've said here, I think you all need to evaluate what's going on. Friction between you and your wife, the drummer and his wife? Is a bit of success worth the strain on your marriage? Please realize that you've already accomplished more than most of us have ever done.
That said, I don't think you're pushing too hard on the "1 a month" rule. Some gigs fall from the sky, and you don't turn them down. I do think that you need to work HARD to confirm gigs with your bandmates before confirming with the venue. I can't imagine that you would ever have trouble contacting your bandmates within 12 hours of any gig offer, max. What kind of opportunity needs a "confirm this second" answer?
People don't like to feel like their lives are out of their control. The singer just got married? Then he's having to adjust to sharing control of his life with his new bride. And now he's feeling pressure to play out a little more than he thought he signed on for- his life is even more out of control. Who would blame him for trying to regain some of that control? I suspect when he said "once a month," he probably meant 6-8 gigs a year (in my experience, most people don't literally mean once every calendar month- it's just easier to say than "once a quarter" or the like).
Bottom line is this- you guys need to rectify your desire for success versus his desire for control and balance that against healthy home lives. The band is supposed to be fun. If you're not happy in the studio and he's not happy on stage, then you may need to change the situation. FWIW, I do like the idea of having him be the non-performing member of the band. Bring on a fourth guy to sing and play guitar live, and then you guys can be a four piece in the studio and on certain shows.
Best of luck!