This is a very big issue for me.
Grandparents shouldn't have any rights, at all.
My parents couldn't give two shits about me, or DH (having told us that) but they still want a relationship with our children.
Sorry, but no. You don't have a bad relationship with the parents, and a wonderful relationship with the GC's.
They act like it's in the child's best interests, but clearly it's in the GP's best interests.
If my children are exposed to toxic behaviour, blood related or not, I'll be making damn sure that the poison source is cut out.
It is MY job as the parent, to protect my children.
Read between the lines in all the stories of estrangement, because the real stories are lying there.