His mother said they are to a few people. The Uncle Dominic mention was an associate to the Colombo crime family in New York who passed away in the mid 90s, still looking for matches. Gennaro and his family are actually connected to the Colombo clan in Sicily. It is possible that Dominic was made in Sicily, came to the states and associated with the Colombo crime family, happens all the time with members coming over still keeping their membership from there but associating with U.S. families.
As for who tipped off about the scam, it is most likely someone close to Robin. Someone who was close to Gennaro is a possibility, but evidence does not add up with that possibility, and I doubt Gennaro own family would have tipped off about the scam.
One inconsistency is how Colombo and Jacobson met. Robin says through Uncle Dominic, but Jacobson has admittedly claims they met at the airport in Atlanta Georgia waiting for their flights. They began talking and thus they figured they could help each other out. It was by chance. After Colombo died, Jacobson took bigger risks and led to his down fall.