Because you're still on the initial 90-day non-B visa stamp, you can stay until that stamp ends even if you're not working. It's only an extension that would be effected by not working.
But you'll likely need to leave Thailand to get a new non-B visa as your current permission to stay was based on a specific employer so you won't be able to apply for an extension based on a different employer from the visa you have.
Each bank branch (not just eat bank) sets their own requirements. Some might require a lease, and some might not. How long that lease is, is also up to the bank branch. You'll want to get a certificate of residence from immigration for proof of address.
Having a tourist visa doesn't mean anything. Visa exempt is tourist entry. Tourist visa is tourist entry. They're calling out people abusing tourist entries, so that visa won't make any difference.
Why didn't they get a DTV if they're doing Muay Thai? That would make much more sense. But now they'll have to wait until their current visa runs out to apply.
Is your wife already in the US? I believe that's a basic requirement.
Last I knew the marriage visa was taking about a year, not years. It's also a much better experience for your spouse because they'll already have their full green card when they get to the US. That means they can start working and traveling immediately and it'll result in much less paperwork and cost a lot less too (by thousands of dollars).