Nanny for one, and Mummu for the other (Mummu is Finnish for grandmother- my grandfather was Pumma)
Thanks for all the input! I never knew there were so many “titles” out there…
I did ask Newbaby what he wanted to call me, asked him who I was, and he waved his arms and kicked his feet, so I’m guessing my new title is somewhat of an interpretive dance movement, which is cool, but it’s going to make signing his birthday card a bit challenging for me.
My daughter would only call her maternal grandmother by Nana- and so that became the norm for both grandma’s, although we always referred to them as grandma in the first couple years of her life.
Mine are/were “Grandmother” and “Firstname.”
The one we were closest to was Grandmother. And if I’ve done the math right, she was your age when I showed up. I’m also fairly certain that she chose to be called “Grandmother.” In spite of the rather formal name, it’s not a formal, stilted relationship.
“Firstname” we barely knew, and in a way referring to her without a title reflected the distance.
I called my mother’s parents Mana (a name I created) and G’Pa. I asked to be called Nana. It’s close enough to Mana without actually taking my grandmother’s name. She died 10 years ago and I still think of it as her name 
I have a multiply blended family.
My mom was Nonny to her grandkids. Her Mom was Gramma (Lastname). Her Dad was Grampa (Lastname). Her stepfather was Poppa.
My father’s parents were Grandma Lastname and Grandpa George (he was dead before there were any grandchildren, so we were less formal about him, I guess.)
My stepdad’s parent’s were Nonny and Poppy, and his grandparents (who were around til I was in my 20s) were Nonna and Papa.
Second stepdad was Grandpa Fuzzy (he had a beard) and his parents were Grandma Betty and Pop.
Stepmother’s parents were Grandma Irene and Grandpa Ray.
My godfather is Greek, so his mother has always been Yia-Yia to all of us.
My husband’s parents are Grandma and Grandpa, but they were briefly Bomma and Bompa 'til the kids outgrew the baby talk.
My daughter’s 18 now, and while she hasn’t started work on any grandchildren for me, she DID give me a grandkitten. He calls me Mew.
My friend Kathleen wanted to be Granny, but her first grandchild couldn’t manage the “g” sound. So now all her grandchildren call her Annie.