In my family, there are specific names for each of the grandparents...
My mom and her husband are Mimi and Grandpa. My grandma is "Grandma."
My dad and his wife are Grandaddy Bob and Gramma Sandra.
But the kids get confused sometimes because Ryan's Dad is also Grandpa. And Ryan's Mom wanted to be called Grandma. And she insists her boyfriend should also be called Grandpa.
There are long periods of time when the boys don't see or talk to Ryan's parents, so sometimes they forget. After his mom's most recent visit, Jackson took to calling her "new grandma" because my grandma was the only grandma he saw regularly.
We ate at a barbeque restaurant on Sunday, and the owner who is a sweet older man kept coming by the table to check on us and talk to the kids. After he walked away one time, Jack said "Mommy, think that is the grandpa that lives with new grandma?" Priceless.