I'd agree that a good relationship with grandparents can be good for kids but a highly conditional relationship with grandparents who shun a parent doesn't sound... healthy. If you are going to police their relationship that is going to have a toll on you and you're well being as a parent is far more important than a relationship with grandparents.
half my grandparents died before I was born, it did me no damage: it's great for grandparents to see their grandchildren but I'm not convinced it's as important the other way (apologies for offending grandparents!).
Good luck navigating this, it's not easy, but look out for yourself.