Harvey, I also think (just my personal opinion here) that sometimes we kind of 'allow' others to treat us in a certain way and that can sadly encourage people who are basically not very nice to just go right ahead and be as unpleasant as they want to be.
In their minds maybe we set things in motion early on that we will accept a certain level of behaviour.
An example I would give to this would be a friend whose father drank a lot (alcoholic) and she ended up always in relationships with alcoholic type men. She kind of expected, and maybe even sought it out.
Now clearly you did not seek out your in-laws, you chose your husband and they just came as part of the package! But do you feel in any way that you have self esteem issues which mean you've given them the impression it is OK to speak or act in a certain way with you?
I am in no way blaming you, I think it may be quite common and many of us do it and get into habits of behaviour with people which are not helpful.
For example, I am overweight and generally so not speak about my weight with people. But the other day on the way into work I heard a radio interview with a singer and she was over weight and a few times she made depreciating comments about herself. I went in to work and found myself doing the same thing about myself! Jokes about too many mince pies etc! How I looked like I liked cakes! Etc.
I did it so much one colleague commented on it, and I kind of laughed it off and said, no, it's just the truth.
Then I thought about it and realised I was kind of leaving myself wide open for negative comments from others because of how I was treating myself. I went and thanked my colleague for pointing it out to me and I've not said anything since like this.
I was just typing this when I saw Chopz comment and I think it kind of makes sense in light of what I have just said. When we act like we expect a level of politeness, respect etc from others we are, I think, more likely to get it.
If we begin to act like we expect to get shit, we may well just get more of it. If they are being so bad to you, you may really need to address this but professional help will help you work out whether their actions or comments are genuinely unpleasant or whether you are being overly sensitive and how to be assertive and yet also perhaps to chill out in relation to them. It doesn't mean we expect shit from people or we put up with it, it means we work out the nomal levels of pleasantness, re-access for toxic relatives and then work out how much we can accept before we say, I will not be home when XYZ are coming etc!
Darkly she said "...came home to see they had left..." maybe she was pleased they had gone if they are so horrible.