For a while there I had Oma and Opa (Oma died this year), Nanna and her longterm partner <firstname>, and my parents ended up Little Grandma and Grandpa without any planning. My partner's mother has picked her own title for herself and her husband, and his father hasn't picked one for him and his wife. We don't see them often enough for them to be called anything other than their firstnames, although I know their other grandchild uses their proper grandparent titles. We see grandma and grandpa quite a lot though - the DDs think Grandpa is the Best Thing In The Universe

I don't know if DD#1 sees her grandmother on my ex's side, I certainly never hear about it. Last time I checked my ex was very much estranged from his mother and stepfather, which does increase the available pool of grandparent titles ...