When my first DGD was born, I decided to be Nana. SIL's mother already had 2 grandsons and was Grandma to them--because HER mother was Nan to everyone. I found it interesting that we both wanted to be different from the other, and worked it out without even consulting each other. Neither of us wanted the "Grandma-first or last name". As to my DH and SIL's father, the girls always know which one they are talking about--Nana's Grandpa or Grandma's Grandpa. The littlest DGD used to call my DH 'Bumpa" which he loved, but she finally learned to say her 'g's'