Daughter doesn’t refer to us as Grandma or Grandpa

I think you just have to follow your daughter's rules. I would never post any photos of my family on social media, without their permission.

Our eighteen month DGD goes round the house, shouting Ga Ga. My children find it amusing and accurate, for I am daft, I find it endearing.
My other granddaughter always called me Gan.
It doesn't matter what they call you, as long as they know you love them.

The other week, when we curtailed her viewing of Hey Duggie, we heard her muttering to herself;,
Oh no, Ga Ga, Papa, no Duggie.. She was not amused.

I had to chuckle at the image in my head that your post brought up.
I don’t ever recall my daughter saying oh look, nanas here
Without looking I don’t think there are any photos of just me and one/two of the grandchildren.

I do not see any problem here. I hope you can put these ideas aside and just enjoy your GC.

I don't think you need to worry, relationships are built on the quality of the interactions that you have with your grandchildren not by what you are called. Take your own photos but don't post on social media without permission and just enjoy the time you spend with your daughter and her family.

To be honest I think none of the above really matters. It will though if you start making a fuss about it. You could take photos of each other with GC but suggest no posting on Social Media without asking your daughter first.

Just enjoy the time you spend with them all