I started out at as just nana, as I was the only grandmother for a long time. When my daughter got a lovely MIL we became NanaX and NanaY (first names). They are old too old now, so I am just Nan. My first great-grand-daughter decided to call me Nanny-noo to differentiate me from my daughter, who is just Nanny, as is my other daughter to her grandchildren.
Given our family history of early childbirth and longevity, I can foresee a day when my daughter becomes a great grandmother and I become a great-great-grandmother, so I wonder what we will all be called then!