Many, many kudos to Geoff, our Don, for posting these photos and i.d.'s. But, Coppola and Puzo were often inconsistent with those individuals and identifications over three movies spanning nearly a century.
In the photo at Anthony's party, the little kid at the far right in the bottom row isn't Santino Jr. In a deleted scene (one of the best, IMO), when Gardiner Shaw is asking Michael for Francesca's hand in marriage, there's a ~7 second bit at the very end (seen only in the TV "Saga" version, not on the "extras" disc in the DVD set) when Michael turns to a hulking young man in a plaid coat and says, "How's the football, Santino?" "Fine, Uncle Michael," he replies. I think he's in that photo in the upper row, right.