Wiktionary
grandparental
a. of or relating to a grandparent
Usage examples of "grandparental".
And that was also the time when I was cast as a ghost in a children's play, and found, in an old leather attache‑case on top of my grandfather's almirah, a sheet which had been chewed by moths, but whose largest hole was man‑made: for which discovery I was repaid (you will recall) in roars of grandparental rage.