Daughter (late 20's) has worked here for several years. Mother was hired in November. They often work the same shift. Boss refuses to put them on separate shifts every time for unknown reasons.
Daughter talks to mother like shit. It's genuinely shocking. Daughter is patronising, rude, shouts at mother, nasty about her skills (still training), regularly says things like "Mum, you're an idiot." and other insults loud enough for everyone to hear. Absolutely horrible. Mother is very quiet and just accepts it. If she was talking to another member of staff like that it would be completely unacceptable. They are customer facing so everyone can hear daughter talking to mother like that.
Boss is refusing to deal with it - "that's just the relationship some mothers and daughters have" - direct quote. I say it's wrong and something needs to be said. They should be acting professionally and daughter should treat mother like any other colleague when they are on the clock together.
I am a manager but with boss (business owner) refusing to deal with it can I do anything?
It's seriously unpleasant listening to daughter for me so god knows how mother feels. When I work with them I spend the entire time cringing and making 
faces.