Our DS children call us Nana & Poppa They call the other grandparents GeGe & Grandpa.
Our other grandkids are step grandkids to me...so they call me just by my first name (not worth the "hassle" with the ex even after 9 years) -- as long as they love us that's all that matters. They call DH Grandpa Charlie.
We have to have a checklist almost when we're signing cards to be sure we get it all straight, lol.