My grandpa’s life partner came into his life after my dad was an adult but before I was born, so she’s been in the family longer than I have. She never wanted to be called anything other than her first name, but by all measures, she is my grandma, and I love her. So I’ve had the typical grandma/grandpa names for mine, but I also have an Izzy, and that’s really special to me.
I just had a horrible thought after reading your last paragraph. The safety law regarding the back seat could be applied to fetuses via a law banning pregnant women from driving or sitting in the front seat, taking away even more autonomy.