I kind of feel for you. I am one of the lucky ones and love my in-laws. Your two older children sorry to say this need to accept that this is not their grandmother, yes she is in their life, but not in the way thay you would like her to be, you can't change that. Sometimes that's harsh to tell kids, but it's the truth and rather than them kepp on getting hurt I would just leave it at that and let them decide. As for your other kids who are her grandkids, I would let her know that you are having a birthday party for your child for friends and then later you are having one just for family, ie them. That way you are taking the drama out of what's supposed to be a happy day. I feel really sorry for your other kids and maybe sit down with her and let them know that they love her as their own grandma and are hurt by her actions. Since their real grandparents aren't around that they thought it would be cool to use her as a surrogate grandparent. They aren't looking for gifts, just love. Maybe that will help her to understand their and your hurt. Good Luck with everything, and remember a woman of her age is already set in her ways and if she's unwilling to change then you need to decide what to do later on.