Quote: If she had convinced my W to change the kids clothes, would the boundary would be what I choose to do in response that that situation?
Yes.... based upon whatever your boundary, in fact, is.
Quote: I guess I see MIL as exerting undue control already over my W. Can I do anything about that, or should I just set firm boundaries on my own responses and let come what may?
Clearly, remodeling is not the issue. The issue is, you feeled ganged up on. Whatever the issue is. Doesn't matter.
Know yourself. Know your preferences, but know that preferences allow for wiggle-room, negotiation. Boundaries are NON-NEGOTIABLE. There is no discussion because it is a matter of YOUR integrity, respect for your self.
Quote: I guess I see MIL as exerting undue control already over my W. Can I do anything about that, or should I just set firm boundaries on my own responses and let come what may?
Is it something you don't like, or something you see as unacceptable? If it is unacceptable, what are you doing about it?
Quote: So if someone is treating you in a negative way, expecting them to change their behavior, or taking action with the intent of causing them to change their behavior is a control issue?
Yes. You can certainly bring your concern to their attention and state your preferences... ask for understanding... but if they decline and continue in the same manner, action is now incumbent upon YOU... if your action is to get them to change... you've got yourself a control issue.
Quote: So then my recourse is to clearly state to MIL and W when negative actions occur that I am unhappy about it and let them decide how to respond?
Yes. They may not respect you, may not be acting like it... but neither are you trusting and respecting them by anticipating their actions/responses and avoiding potential conflict.
