Grandpa Who?

I just asked Michael to tell me his Grandmas' names. He responded with Grandma Sandy, Grandma Sue, and Grandma Decker. I asked him to tell me the names of his Grandpas and he responded with Grandma Sandy's Grandpa, Grandma Sue's Grandpa, and Grandma Decker's Grandpa. I laughed pretty hard. I guess I need to help him to learn their names.