Oh dear they do sound like a sad pair! Some people, I guess, dominate their children as they are growing up and then want to carry on leading the clan and getting all their own way when their children are adults. This does not often happen in these days of nuclear families. It may be the natural order of things in many cultures, but it ain't round here. This may leave grandparents who feel like this (esp if they are retired and don't have other stuff to dominate) in a state where they want to continue to be in control, and can't come to terms with the fact that they aren't. I feel sorry for them that they are not more self-aware and sensitive. They are going to get less contact with their GC if they don't "cop on".
Just a thought - some people as they are growing up assert themselves as adults (it could be teenage rebellion, cutting loose in your twenties or whatever) This is the moment at which most parents start to get the message that they are not in charge any more.
(I remember losing my temper with my mother for the first time ever - roared at her to "FFFing shut up and stop going on at me", while driving, and nearly crashed I was so angry. I was in my 40s. Late developer. But it was definitely overdue.)