When the Younger Chick was three, we had a simply ghastly three weeks with him in hospital, and not necessarily going to come out again. The Elder Chick was five, and we had no family close by. First my mother and then my MIL came to stay (my FIL came too but he was about as much use as a chocolate teapot), and they ran my household for me, so that DH and I could be at the hospital, the Elder Chick could go to school, there were meals and clean laundry etc. etc. cont page 96. Boundaries simply had to be shifted, or indeed abandoned; if somebody didn't do my laundry for me, I had no clean clothes. If somebody else would make a meal and collect the Elder Chick from school, DH could make an appearance at work and at least tell other people what to do. My MIL eventually said to me, 'dear, I don't know how you do things, so I'm just going to do them the way I normally would rather than asking you all the time, all right?' and I simply nodded. There's a time to worry about somebody else cleaning your lavatory, and this wasn't it.
Afterwards? I could find nothing in my kitchen, because between them, my mother and my MIL had put things where they expected to find them - someone else's kitchen is never laid out precisely the way you would do it yourself. There were several things one or other of them bought because 'well, I know you must have one, but I can't find it, so it was easiest just to get another one.' I don't think I ever found where my MIL had put the potato peeler, but it didn't seem terribly important; I put it on the shopping list.
After it was all over, it wasn't the easiest to reform the boundaries. Easier for my mother - as somebody said upthread, it's different with your own mother to how it is with your MIL. On a visit to my ILs later, I 'helped' my MIL turn out a cupboard, and in retrospect, I think there might have been a degree on my part of... boundary pushiness, shall we say. She didn't hold it against me, but the degree to which either of us was completely 'at home' in the other's house, the things we could do without asking permission, was... odd.
Intent, in our case, was all, I think.