I have no recall of either set of grandparents. My father's parents had passed before I was born, and my mother's passed when I was barely a toddler.
My kids called both sets of grandparents Grandma and Grandpa.
My granddaughter calls me Grammy. My ex and I split when she was very little and just starting to talk, but she called him Poppy. She calls her other grandparents Oma and Granddad.
My grandson calls me Grammy. He doesn't know my ex at all. He calls his other grandparents Mom-mom and Pop-pop.
If my ex comes up in a discussion between the adults and the grandkids are present, he is referred to as "your grandfather".