I read it in the late '70s or early '80s. It was about a girl, possibly called Persephone, who lived with her parents and ?brother? above a chip shop. There was a sister who went to a boarding ballet school. The brother also had a talent, but the main character did not, so people always said that she had beautiful teeth. The other siblings did too but they also had other talents whereas she did not. I think she had the attic bedroom.
Any ideas?