This means pausing his mom's naturalization though. And who knows what would happen to fees and processes in 2 years from now.
If his mom naturalizes now, he'd be a citizen without a question.
You don't have to apply for N-600 immediately. He can get his passport first. But N-600 is ultimate proof of citizenship, and better be done sooner than later. The more time passes, the more difficult it becomes to prove his citizenship.
Here's example why N-600 is highly recommended:
TLDR: he may be required to prove he's a US citizen at any point in future. Maybe long after you and your wife are gone. Proving with certificate of citizenship is 1000 times easier than trying to find all evidence of his mom becoming a citizen after many years...