DH's parents were given their 'names' by DH, he called his grandmother and grandfather Grandma and Grandpa so it was just automatic for him I think.
My mum wanted to be called 'Mamie' as it was her great-grandmother's name. I nixxed that. Mamie is a brand of noodles. I just couldn't come at that lol. My dad is Pa although that was just something automatic again. I didn't even really consider it if I'm honest, Pa just seemed to suit him best lol.