My mother's mother is named Dorothy
My father's mother is a little bit complicated.
She's always just gone bu Joan as a nn for Josephine, thinking that that was her first name but then, when applying for her first passport a few years ago she discovered that her Birth Certificate, Marriage Certificate and Christening Record all had a different name on there for her(which was absolute murder to explain to the Passport people!). She's Catholic and Irish so the Chirstening Record is considered the most valid so I think that's what she went with. They all say a different combination of Siobhan, Bridget, Brige, Josephine and a couple of other names I can't remember!