The person next to me at check in at Heathrow was asked to show a flight leaving Thailand as he had only booked one way with Emirates. Don't know how it got resolved as I finished checking in before he did.
You will only need the TM30 from the hotel you're staying at when you go to get your extension. On the basis you're not doing the extension whilst staying at your current hotel I wouldn't worry about it.
I'm guessing it depends on whether his wife is Thai or not. My wife couldn't work on her dependent visa and had to get her own extension of stay based on employment, at least that's what her employer told her anyway.
the international schools I visited when looking for somewhere for my kids all wanted to see what visa my kids were on. They were my dependents so no issues but if on visa exempt/overstay then it might be a problem.