I'm sorry, cpatlew. That sounds very painful.
One needs to understand he bad mouthed her for the first 8 years of their marriage but didn't leave her. He enables her and overlooks her down right mean character.
For whatever reason, though, your son has chosen her as his partner. I can only imagine how tough that is for you, and how difficult it is to understand (I wonder why my father chose my BPD mother, but that's another conversation).
Have you heard of Radical Acceptance? (
Radical Acceptance for family members). That might be helpful for you to read.
It's certainly part of the grieving process to be angry. If you want your son and grandchildren in your life, are you ok with keeping your door open to them, even if it means that you have to include your DIL?