I don't see how the quiet time should be an issue, you can look up plenty of articles on children and nap time that say when a child is done with naps you know, because they don't want to do it anymore and quiet time is what almost all of them suggest. My 4 year old doesn't nap at all anymore and hasn't since she was 2 1/2 - 3. However, if he doesn't nap and ends up going to sleep way earlier than he should and waking up again when he should be going to bed, I could see that being a problem.

I don't see what the issue is with you two sharing a room or why they should have a problem with that. If they don't have a legitimate reason I'd tell them that it's not a good idea right now, and until they can think of how it's negatively affecting him they shouldn't request that.

You definitely shouldn't cave. You're raising your son too, and your opinion is as important as theirs. As far as confrontation goes, maybe try an email or text first?

You have to stand your ground on some of these things, or else in the long run you may regret letting them make all the rules and decisions. There could come a time when their defense is that you didn't have a problem with blank rule at first, why do you now?

I hope that helps and you get everything straightened out! I know it's tough to be the one who gives in and lets others make all the decisions with your child when you know what you want done.