I had two Nanas and two Grandpas when I was growing up; we simply added their last name to the title. When my turn to become a grandmother came, I didn't want to have the same name as anyone else so that no other name would have to be added -- probably silly, but that's how it is. Anyway, I'd wanted to be Nana to follow my family "tradition", but the other grandmother was to be Nana (pronounced Nahnah, since it's in Spanish), and I thought that might be confusing, especially since DMIL is Nanny. LOL! So I eventually became Mémé. Can't find cutesy little coffee mugs and that sort of thing with Mémé on them, but who cares? I'm using a not-common-in-these-parts name, and that makes me unique. :D
OTOH, DH is Grandpa, as is the other grandfather of two of our DGSs. DH is Grandpa, and the other one is Grandpa + first name. Works for us. :)