I called both my grandma's, grandma.. Although, when at home, distinguishing between them, by dad's mom, I added her first name to Grandma. but, to her face.. just grandma
I called one grandpa... grandpa... and my other grandpa Linwood.. because that was his name. He was a step grandpa, but joined the family before me.. I call my own dad by his first name.. frankly, nick names just weren't used much.
Anyway.
My kids.
Call both grandma's.. grandma.
Call my dad "Grandpa Pete" (remember, I call him by his first name)
Call DH's dad "granddad"