Grandma, grandma-grandma, grandpa (oral)
Grandpa, Grandpa-Grandpa, Dad (spoken)
Dad.-Dad
Mom.-Mom
You can call your grandchildren and children by their first names ~
It is very important that even children of foreigners will not call their parents by their first names unless they are "step-"(half step/half step).
I hope I can help you! ^_^