Names for great-grandparents?

Layne
My parents have decided they want to be called Grammy and Pap. All 4 of my grandparents are living and I call them Grandma and Pap Pap using last names if I need to distinguish. I'm not sure what to have our child call them? Great-grandma and Great-pap? That seems like a lot for a little kid but the only other option is new nicknames altogether?