DSD calls my parents grandma and grandpa (as that's what my dd has called them), but calls me by name.
DD calls DF (stepdad) her dad as bio isn't in the picture (her choice as she wanted to be like her step sister and younger brother). She calls his mum and stepdad "nan" and "grand-da" (like the other kids - DF calls his stepdad "da"). She calls his dad and stepmom "grandad" and "gran".
Then to get even more confusing dsd calls dd's paternal grandparents "nanny" and "poppy" like dd.
Basically just use all grandparenty names regardless if bio related as just too difficult. Dd originally had her own names for DF's mum and stepdad (we see them often and she nicknamed them hoho and lulu) but chose to just follow the other kids.