I am glad this was decided this way and it seems to me it would have naive for the Grandparents to expect things to turn out differently. I have personal experience in this area with me forbidding my parents from discussing religion with my children when they used to come and visit when I was at work. I made it very clear that if my wishes were not followed the visits would end.
My wife and her family who are not Witnesses thought I was being a bit harsh, but they didn't understand the cult intricacies the way I did. So instead of trying to recruit my children they concentrated on my wife for a while but without any success.
Someone at the Kingdom Hall must have advised them not to pursue Witnessing to my children and because they did not discuss religion with them they had an almost normal Grandparent Grandchild relationship with them for a while.