Euh.. I don't speak English to my parents of course..
But I use the Finnish words "äiti" and "isä" which mean just the usual "mom" and "dad".
I have always called my grandparents (from my father's side) by their first names. That's kinda funny. They asked for my sister and me to do so cause they would've felt themselves old if they've been called grand parents or something.. In my opinion that's silly. When I talked to my friends about them I always talked about my grandmother and my grandfather..