I always called both sets of grandparents just grandma and grandpa... no name following.

Hannah doesn't call them anything yet but my in laws want to be called "Grammy" and "Granddad" although my MIL wants my FIL to change his to pop pop or something lol. she asked what my parents wanted to be called and I was kinda like "uhhh... just grandpa and grandma" I always thought everyone called their grandparents that unless it was like german or something where there is a name in that language that you call them lol.

so my mom is grandma, my dad is grandpa, my step dad is papa (that's what his grand kids call him so we followed suit) my MIL is Grammy and my FIL is granddad unless my MIL can convince him to change it lol