Thanks for all the replies. I'm actually a bit sad that my family can't get their act together.
My inlaws can be problematic, my mother is right, they are thoughtless. However, it's been 10 years and she needs to stop complaining that they "slight" her. She seems to think that they are purposely doing it to hurt her. They aren't. She doesn't factor into their thoughts at all which, I guess, is the problem.
The latest drama is that my inlaws didn't send her a sympathy card when my grandmother passed away. My MIL did express condolences to me and she did tell my DH to tell my mother how sorry she was. However, mil didn't call my mother personally nor did she ask to personally speak to my mom when she was on the phone with my DH.
Now everyone, including my DH, agrees they should have at least sent a card. But really why so much drama over them? I have cousins who didn't call, show up to the funeral or even send a card. My mom isn't livid at them. It is just my inlaws.
My inlaws aren't thoughtful. They forget my DHs birthday. I just wish my mom would stop taking it so personally.