My wife was very careful to negotiate these things when we had Sarah. Her mom did not want to be a “Nana” so became “gramma.” So the wife’s side was Gramma and Pappy. Mine were Grammie and Pop Pop.
My Mother is Nana - we don’t have another grandmother in the picture so that is all my children have ever had. The GiGi thing was more of a joke than anything. No children on the way and usually kids decide what they call their grandparents anyway. It kind of falls to the oldest grandchild.
My family got into a similar problem: My parents were always Grandfather Cook and Grandmother Cook to our kids; St Ronnie's were Grannie and Pop. No problems, everybody was happy.
But, when we grew up - though some here would wonder if I ever really did grow up - our oldest had babies anf things suddenly became more compicated. St Ronnie also wanted Grannie though, but I got Grandpa. Our “in-laws-in-grandparenting” choose Nana and Papa, and Jackson and Ainsley grew very comfortable with all the names they used. ... Until St Ronnie's mom came to town.
She knelt down and told Jackson that “My name is Grannie. Come give me a hug.” He jerked away immediately, ran back to Ronnie's knees and hid behind her in shear panic. “No! No! You're not my Grannie! Grannie is my grannie!”
Took a little while to get him calmed down, but he (eventually) agreed that this strange woman could become “Grannie Gail” ... just as long as HIS “Grannie” was going to stay “Grannie” and not be replaced by somebody else.