Thanks for the responses.
I assume that the grandparent's band in question would have to be activated by said grandparent at the entrance to the park?
Edited to add: More specifically...family of 4 and 2 grandparents all make FP reservations for DHS, either in morning or evening. In afternoon, all park hop to Epcot and ride Soarin standby and mill around park. Family of 4 wants to return to DHS for evening FP's, including using grandparents who are returning to hotel. Do grandparents have to return to DHS to "activate" evening FP's?? Or since they were already in DHS once during the day, is that enough, even though they were last in Epcot?