I only had one grandmother and we called her Mammaw for years, then we switched to Granny. DH had Granny and Paw Paw. Our children call his parents Nanny and Paw Paw, and my dad is Grandpa, (my mom passed away before I had children). Have no grand children yet but DH and I have talked about what we would like to be called and he likes Granddaddy and I Grandma or Mammaw...I'm sure it will just end up being what ever that first grand comes up with.