In our family, we couldn’t pronounce these so it was Ubbie and Ummie.
Mine were Papa (mother’s stepfather), Granddad (father’s father), Granddaddy (mother’s father), and Grampa (stepfather’s father).
My father is called Grampy. I like that one.
My maternal grandfather is avi (catalan, pronounced AHbee), the paternal one was abuelito (ito when we were too little to pronounce it).
The Nephew calls his grandfather “ahlo”, a mispronunciation of abuelo. For some reason he seems to like the ends of words.
The Kid couldn’t say “Grandpa” - came out “Gah-WAM-pa”. So that’s was his new name. Gwampa. He was also Bampa. Bampa Bob. Sounded good.