Reading these stories, I think I have to accept that I probably trampled my MIL's boundaries a few years ago.
MIL and FIL were on vacation when a medical emergency caused them to have to remain out of state for 10 weeks. BIL had been staying at their house while they were gone then he and my DH flew up to help MIL and FIL travel back home. DH asked if I'd go by their house to make sure everything was in order, since we knew BIL wasn't the best housekeeper. And in recent years, MIL hadn't been able to do as much house cleaning as normal so things had already gotten a little out of hand, not bad but things like baseboards not cleaned, cobwebs in corners, doors not wiped down and rust in the bath.
When I got there, BIL had left a complete mess. Newspapers everywhere, pizza box on the counter, soda cans on the coffee table and it didn't look like any dusting or floors had been done since she was gone. When I checked the fridge it had a really bad odor.
So I ended up doing a whirlwind cleaning. After reading these I think I probably should have stopped at just throwing out the garbage, putting fresh sheets on the bed and dusting and doing the floors. But I cleaned out the fridge, throwing out things near expiration and cleaning it completely, cleaning all the doors, baseboards, and cabinets, cleaning all the light fixtures, light switches, and windows, vacuuming under the furniture cushions, and giving their bathroom a thorough cleaning, removing all the rust stains. And their bathmat had mildew I couldn't get out, so I went a bought a new one and some pretty hand towels to match. (I did leave the old one in the linen closet.)
I don't remember MIL ever really mentioning it. I do seem to remember her thanking me for stocking the fridge with fresh groceries and for "picking up after BIL" and for the pretty bath rug and hand towels. But now I wonder if I might have really offended her.