Called both grandmothers Mommee (both syllables same accent, not first like Mommy). Have no idea where that came from, but all the other cousins used the same, and had much older cousins on both sides. I was raised in Dallas, but parents, aunts, and uncles raised in Sherman, where my grandparents lived until they died. Maternal grandfather was Grandad, paternal was Poppy. Called step grandfather and step grandmother by their first names, Arthur and Frankie.
Wife is Granma. DIL wanted something different for me. Oldest grandchild born about when Sean Combs changed his name from Puff Daddy to P Diddy, so she started the granddaughter to using G-Daddy. That's evolved to Gee. All grandkids use that for me.
As a side note about adults using childish monikers, my dad and his sister called and referred to each other as Bubba and Baby until their deaths (age 82 and 90) Grandmother (Mommie Reynolds) called them that until her death, in her eighties.