Ernest Coulson was my great-grandfather (Charles Thomas Coulson my great uncle)
There is a family history with the Coulson's giving each other nicknames different from their christian names. Looking at the photo though I don't think Andy can be Ernest. Ernest wasn't born until 1880 so there was quite a gap between him and Charles.
Andy might possibly be Alfred though - Alfred was another of the brothers and closer in age to Charles (born 1868). I can't be sure but just a thought!