Not all grandparents do take their DGC for sleepovers. Others are far from the Grandparents, so it's not possible.There are probably some parents who would be delighted even if only two of three are taken at once - better than none at all. Maybe the parents should appreciate the offers they get, even if it doesn't always meet with their approval, and be prepared to negotiate, pleasantly, if there is good reason to do so. As long as the younger ones get a turn, maybe even giving them first turn, making sure they know they're not being left out.