I usually just kind of lurk around here, but Dove the issues your facing with your in laws sound so much like the ones I had I felt like I needed to comment.
My marriage is a second marriage for us both. We both came into it with children from our previous one, then we had children together as well. My in laws lived a 3 hour trip out of town so would only make the journey every 4-6 weeks for a weekend usually. I used to dread that weekend they'd be here. My MIL was so mean and spite full to my children, it really felt and seemed like she would go out of her way not to do things out of love for her grand children but rather to do things to taunt my children. All weekend I would have to sit and bite my tongue and try my best to tolerate her. I found myself despising their weekend visits. I begged my husband to say something to his parents, to stand up to them. And in my eyes, although his father wasn't nearly as bad as his mother, he was also guilty as he would permit these attacks.
After their Easter visit this year, my husband and I had a HUGE argument, something that had never happened to us in our 3 year marriage. I'm talking a full on yelling match. I was frustrated that he wasn't putting his foot down and putting an end to this. He kept telling me that they were old and set in their ways, that saying something would only cause upset & turmoil.
Last June I found myself again facing a weekend visit, 8 months pregnant with our now 6 month old daughter. Maybe it was the hormones, who knows, but I decided enough was enough I just couldn't tolerate it any longer. I would never ask my husband to choose between the parents that gave birth to him and raised him and me. I couldn't do that but felt for my own sanity, I needed to remove myself from the situation... so I packed up my kids and went to a friends for the weekend. My husband asked me not to go, and wanted to know what he should tell his parents when they asked where me & the kids were... I told him he was NOT to make any excuses and if they asked, he was to tell them the truth.
He did.
The weekend following their visit, we received a call from my father in law that his wife had been diagnosed with cancer and would be beginning treatments immediately. He didn't know when they'd be able to visit again.
They did manage to come for one more visit, when the baby was about 10 days old. After everything that had happened their last visit they opted to stay at a hotel and asked that we bring the baby by, since they didn't feel comfortable coming to our home. We did, and for an hour (possibly more) his mother held her new grand daughter and wept.
Two months later she passed away.
There really isn't a point in me sharing this. I do know that if I could take back that weekend of their last visit when I fled to a friends house, I would. My ending may be fairly dramatic, in that I never got a chance to make things right with my mother in law. I'm glad that I did finally stick up for myself, in that I let it be known that I wasn't going to tolerate being treated this way, but clearly my approach was all wrong. I'm also not going to have a chance in this life time to make that right.