Book about Musician who Marries Sister maybe Unknowingly?

I am trying to find a book that both my wife and I read. She remembers it well, but me only peripherally. IIRC, it was about a musician. He falls in love with a woman, and I can't recall if it's early in the story or at the end, but I believe that his first love falls ill and he then falls for the sister. I believe that part of the story at least is in Prague. Again, not sure, but IIRC, the big reveal is that the one sister caused the others sickness to 'steal' the husband...

Been a long time since I have read it. Any and all help welcome! Thanks!!!