I have been with my DH for over 30 years and we are both in our 50's. For the whole duration of this time, I have not had a good relationship with my in-laws, in particular his mum.
The things my MIL says to people, including her own DC, are very nasty, and damaging. His mum is also a game player and very controlling. There are too many things to list here, but take it from me, she is very dangerous.
So, as my MIL has aged she has changed roles from toxic bully to ageing, frail victim with Madonna status, who cannot be upset by anyone. In the past my DH has admitted that his mum is nasty, but he never did anything about it, making it more difficult for me to stand up for myself. Now, however, he feels really sorry for her as she is getting old and frail (not so).
Here is where the "at odds" are coming through. My DH wants to visit them more and do things for them, whereas I am the complete opposite. I am older and wiser now and I feel that his mum is not good for my MH. I hold deep resentment and a massive grudge toward her. I do not want to hang out with her or his extended family who sat by and let her treat me that way and even stood up for her when I pulled her up in the past.
When I rarely see MIL, I am friendly and polite whereas she is offhand with me. For example, she always comments that she is not invited over anymore, or included in things, and these things are always directed at me, not DH. It's my fault.
My DH is upset as his parents are coming over tomorrow to drop something off. It is my one day off before a stretch of 6 working days and I have plans. Why can't he see his parents on his own? I think this is perfectly normal. I see mine on my own and my brothers visit my parents on their own all the time. Why do I need to be there? DH doesn't want to upset his mum as she is ageing and frail (she's really not) but I have zero empathy or compassion for the woman.
I can see this being an issue in the future as my DH can see that I just don't care whereas he has gone the opposite way, which I understand as it is his family. I don't voice any of this to him, but he knows as I make zero effort with them now, whereas before I treated them the same way I treated my own family.