nananina if anybody wants scissors, cream, cotton wool etc while they're in my house they are very welcome to ask for it and they will get it. They are NOT allowed to go hunting for it themselves. This applies to every single person whose home is elsewhere.
Reading cards and letters that are not addressed to you is absolutely morally (and legally, when it arrives via mail) wrong. Lying around means lying around for me, and the people who live in my home. I take just as much offence from my MIL reading this stuff as I would a friend, my cleaner, the dishwasher repair guy or anyone else whose home is not mine. The fact that your family all do this, including your DILs, means that it's a very good thing I am not a part of your family.
I stopped writing messages to my SIL and BIL because - seeing as you ask - the latter contained reference to some strife he had suffered with his parents. This was written to and for him, not his mother, but she took it upon herself to invade his (and my) privacy on a matter he had chosen to confide in me about (and not his mother). I will not risk that happening again, and because I stopped for BIL I must stop for SIL.
Yes, I am the controlling force. In my house, you better believe it. In her house, I absolutely am not. FYI there are rooms in her house that even after all these years of marriage I have never even had the nerve to step into (her bedroom, bathroom and dressing room, specifically).
And yes, I am talking about an adult, a 62 year old one. I am giving her the treatment she earns. If she behaves like a child I will treat her like one. If she behaves like an adult I will treat her like one. And I absolutely expect her to do the same for me (and she does).
As for my MIL's relationship with my DC, it's absolutely wonderful. She's an absolutely brilliant grandmother, and she has been wonderful in respecting my boundaries as the mother. She hasn't once done anything that has caused me offence or overstepped the boundaries. I am extremely lucky that she is my DC's grandmother. Honestly.
Finally, the reasons why I won't say anything to my MIL and will just suck up the behavior and come on here to rant are (1) my DH doesn't have the headspace to deal with this issue, and I am absolutely fine with that (2) ultimately, like I say, she is a good woman. I have my faults, so does she. We both keep our gripes to ourselves (3) I hope to have her in my life for as long as she lives, and I want a good relationship with her. She has been extremely good to me throughout my marriage. On balance, I lucked out with my in laws (4) see above re relationship with DC
I appreciate your valiant attempt to defend MILs everywhere, but in my case it's a lost cause. At the best of times this is a nuanced relationship. Nosiness and boundary-overstepping is frankly not that big a deal compared to what some people have to put up with.