OK I'm not a grandma (thank goodness) but...
When I was born, my grandparents decided that my mother's parents, who lived closer, would be "Grandma" and "Grandpa", and my father's parents would be "Grandmother" and "Grandfather".
I called them all "Grandma" and "Grandpa". I was stubborn.
father in law is "Papaw", and mother in law is "Grandma Mary"... Biogma is "Grandma Ann" and my mom is "Grandma Jane". To Belle and Pat. To Rose... Well, due to the family feud she doesn't know mother in law (not since she was 5 months old), has barely seen father in law (Since she was 11 months)... And my parents are "Gama" and "Gapa".
sister in law's grandsons call her "Mimi".