Well.....congratulations Gramma and Grampa to be!
My grandchildren call me MOM or Gramma.
Both sisters of mine who have grandchildren have their grandchildren call them "Nana".
My stepson calls his grandmother "Nana".
My grandchildren from daughter number one call their "other" grandmother "Ganny".
I've even known some grandmothers to insist their grandchildren call them by their first names because they don't want to be called anything that reminds them they are a grandparent.
Being a grandparent is an awesome responsibility, and I couldn't be happier. As a matter of fact, number twelve is on its way the first part of February.