AIBU - my brother is in a relationship with a woman who had a kid that was about 12 when they meet. Let's call the kid Nancy. Not sure where the father is, but the mother is a piece of work.
Some time after they were in an established relationship Nancy started to call my parents granddad/nanna. Nancy has since had a few children, who call my parents Great grandfather/Nana etc.
My parents don't like being called that because they don't think of Nancy etc as their blood etc.
My brother has no blood children with the women and I don't think she calls my brother dad..... so why call my parents granddad etc.