Quote: What I need is a way of expressing a clear boundary to my MIL without creating the mess that can easily happen with ILs.
1. How combative is your MIL?
2. You do realize that you have absolutely no control on how your in-laws will respond?
I have a hard time with #2 personally. I couch my verbal communication in southernese and twist myself up in knots trying to find the best way to address something when my conflict-avoidance issues are screaming at me.
My point is - it's probably going to hurt. Once you accept that as a very distinct possibility, you might be able to push past your tendency to CA and follow through.
Notice your MIL went to your wife both of these times knowing that you could overhear her.
So, stop pretending you don't hear her.
Quote: MIL then walked into the other room where W was and proceeded to try to convince her that it was too chilly for skirts and thus the kids needed to be changed into long pants.
Step into the room, and say, "MIL, I appreciate your concern for the kids, but as I said earlier, I don't think the temperature warrants changing their clothes."
Then step back out to whatever you were doing in the other room.
Quote: Another incident occurred in which MIL was dicussing house remodeling with the W within obvious earshot of me, trying to convince her of some remodeling that she already knew I didn't approve of.
I assume that you and your wife had already discussed the renovation and had agreed that you weren't going to do it. Based on that assumption, "MIL, wife and I discussed this and have chosen not to do X."
If you and your wife have not come to an agreed upon solution, then it's, "MIL, wife and I are still discussing X and have not come to a decision yet."
