Hey
Welcome on board!

)
Well, my parents were introduced by their first names. As Ss9 spends much time with my mom (she's at home when ss comes home from school and waits for dh or me to arrive so ss isn't on his own), they have a really strong bond and depending on the situation, he calls her "grandma". Mostly in public though, because he hates explaining his familiar situation to other people. As for my dad, they sometimes meet and do stuff together and he sometimes calls him grandpa, also depending on the situation. It was up to ss (and still is) to choose how he calls certain people in his extended family, but we always introduce them by their first names and say something like "this is xy and he is something similar to your cousin/ aunt/ grandparent from catclaws family's side".