Good question. I would think Mike being so paranoid that he would kill his brother who was not a bad guy he would definetly kill two killers who aligned themselves with his enemy. The thing is we dont know what happens to the crime family structure at the end. By part 3 we know Mike doesn't take part in the criminal part of the family anymore. Does Mike still run the criminal empire throughtout the 1960's or does he relinquish his control.