I think when you are at a stage where you can't communicate well, you don't really know the person any more. That leads to assigning motives that might not be there
You might be thinking your grandchildren have been weaponised (I still dont like that or think its healthy but hey ho) against you
They might be thinking that they are protecting their children from having any part in a broken relationship with people they cannot get along with.
Most people who estrange feel right to do so. Whether you agree they are right or how you feel about it doesn't change that at all, they felt strongly enough to walk away.
If you are looking to assign the worst possible motives to their decisions, it won't help resolve things with them and when you move past a place of wanting resolution, it won't help you to hold on to motives you cannot be sure of, that can only hurt you now... your opinions of their motives can't hurt them or impact them, they stopped hearing you.
So maybe some things need to be let go of, for yourself. It has nothing to do with them, it's your life and potential for furniture happiness that matters now