Another thought on the sibling--maybe the sibling was injured and became mentally or physically impaired and Rossi blames himself for it (whether he should or not). There's a movie with a similar story line, Dominick and Eugene--starred Tom Hulce (Amadeus) and Ray Liotta--wonderful little movie.

I'm with you in hoping that they don't go for the obvious bit of it being Rossi's kid...a niece or a nephew would be better... it being his sibling would make it more interesting, I think.