This probably won't be an issue for some time, but knowing my extended family it eventually will be. If the subject does come up, I know that there will be a ruckus no matter what I say, but I'm trying to figure out a way to run damage control.
Here's the issue: things have mostly been swept under the rug with my uncle and his family, and my mother is on speaking terms with them again. Things are okay, but I stand by my decision to only interact with them when we happen to be getting together. Recently, my mother agreed to watch my two little cousins, aged 3 and 1. To say that the 3-year-old is busy is an understatement, and though I love the kids to death, I wasn't pleased that I got roped into being "hands-on" when it was my mother who had signed on for it. The 3-year-old, who still isn't potty-trained, took off her wet pull-up and sat on the couch before I could stop her. I was really out of my element there! Babies I can handle, but the older one wore me out. We discussed it after the kids went home, and she said she would respect my decision next time. Yeah...we'll see.

Thing is, when their parents came to pick them up (an hour late, but we expected that), my uncle mentioned having the kids sleep over one of these nights. This is a problem for several reasons. One, we don't have a spare bedroom, and the 3-year-old won't obey. Two, the dog and cats would be upset. And three (because my grandmother once said, "Oh, she can stay in CrochetFanatic's room" the last time the subject came up), my room is a child-free zone. I like my privacy, the bookcase is not anchored to the wall, and I've got all sorts of things that I don't want the kids messing with or breaking. In short, an overnight stay is
not gonna happen!
So, here's my question. We're going to say no, because it really doesn't work for us, but I'm trying to think of a polite way to put it that will be less likely to start something, and doesn't involve JADEing. I can see it now...
Me: My bookcase isn't anchored to the wall--
Them: Well, can't you just
anchor it to the wall, then?
First of all, it's not my wall. Second of all, I don't tell them what to do with
their living space. Would it be rude of me to say, "Sorry, I don't want them going in there."? Please don't interpret this as my saying the kids aren't welcome. They are, the just can't spend the night.