Conversation so far:
How did Dion DiMucci end up in the Belmonts?
Bob and Gene Schwartz also signed Dion's friends, the Belmonts, (Carlo Mastrangelo, Fred Milano, and Angelo D'Aleo), a vocal group named for nearby Belmont Avenue.

Question: Who else was signed?
Self-contained rewrite: Who else was signed other than Dion DiMucci?