My great grandparents were a case of this pre WW2 - my great grandmother converted to Catholicism and her father never spoke to her again. Her siblings weren't supposed to have anything to do with her, but they did come to visit. In fact her sister married my great grandfather's brother, and in this case he converted to the Church of England. This only turned up when my aunt did some digging on the family tree, which seems a little odd, since you'd have thought the two families would have had a lot to do with each other. It made me wonder if the Catholic side cast their own convert off.