[GGG]

I think some of this is on you.

You wanting them to clean up seems kind of ridiculous 6 months after the fact. It would have been nice of them to do it as part of moving out but expecting them to comeback and clean a bathroom and resenting that you had to spend an hour cleaning the bathroom seems like your problem rather than theirs.

The issue is that the line between tenant and house guest is blurred. If someone came for a weekend you wouldn't expect them to clean the bathroom before they leave. When they go from house guest to tenant is different for each person. So I think if you want them to clean up you are in for a world of resentment. And whether or not your inlaws deserve you to clean for them or not doesn't really matter. Your resentment over the situation is not healthy for yourself.

Ask yourself what you want out of the situation.

Do you want your inlaws to realize the error of their ways apologize, clean your house and remove their stuff and thank you for your hospitality.

Or

Do you want your rooms in your house back?

One of these things you can have easily, the other you will never get and hurt relationships trying fo get. So you need to decide if winning is more important than happiness.

That said I still wouldn't box up their stuff, just a deadline then the dumpster.