I've read and reread the posts on this subject, including mine. I'm just so sorry you have to go through this. I guess after losing my FIL and with step-MIL in nursing home, and my mother of 83 years in not the best of health, I'm realizing life is so short.
Have you tried writing her an honest, non-attacking letter? I feel sometimes a letter instead of a confrontation can work really well. I would put everything in it that you posted, including reminding her that she took her hubby away from his mother too. Maybe someday she can enter her grandchildrens life again, there is nothing in the world like grandparents (if they are good grandparents). You don't ever have to be best friends, but if you let her know just how much you love her son, maybe her heart will soften.
I wish you and your family the very best, no matter how you chose to handle it.
