I will assume both couples are married couples? If not then may be a bit more complicated, you mentioned granddaughter and husband so proceeding on that basis:
An EEA “family” member (Descendant or ascendant) with pre settled status would have a right to reside based on status of another EEA “worker” (Or any of the other relevant statuses) family member (As in the days before Brexit) if they are dependant on the EEA with a relevant and appropriate status.
A family member would include those mentioned so far. So in answer to your questions
1. Yes
2. Yes, unless you have enough other work history for either or both, or anything else to confirm a current right to reside.
3. The Granddaughter and husband are not “sponsors” in that sense, they are dependants of EEA citizen/s with a right to reside and pre settled status, and the grandparents are dependant upon them which means they have a right to reside if the rest of the stuff fits.
