Carolyn says most of what I would say, except for one big one:

Lady, for all that is holy, find something to do with (some of) your time and energy that isn't related to your grandchildren. Volunteer. Take craft classes at your local Michaels. Get into college football. Watch true crime shows or listen to horror podcasts. Just find something that isn't all about being a grandmother. Everyone, but particularly you, will benefit from this.