My first son was the first born grandchild on both sides. He has two great grandmothers, 2 grand mothers and one grandfather.
He chose to call my Mum Mama, may Dad Par-Par, his paternal grandmother Grandma Roberts (yes both words). The great grandmothers were Great Granny and Grandmother Roberts (no great).
My second son was the first grandchild on my husband's side. His grandfather is Grandpa Bill, his grandmother, Nana or Grandma Nana. His step grandma is Auntie Diane. Grandpa Lloyd (dh step father) passed away before our DD was born.
Now the kids also have Granny Paddy (my step mother) and Grandpa David (my mother's partner).
We have multicultural grandparents, Granny Paddy is a New Zealander, Grandpa David is from India, Grandpa Bill lives in the Uk with his English wife who the kids call Auntie Diane.
My red head, blue eyed freckled son loves to tell people his grandfather is Indian. He classmates do not believe him, until they meet David.
Often the child will determine the name for the grandparent. I was the first born on my Dad's side and could not say grandma and already had a Granny. I called her Mar-mar. Dad was thrilled when my son called him Par-par.