Vito and Michael were orchestrating Barzini and Tattaglia's murders. The rest were Michael's doing. The fifth family is the Bocchiccios. In the book the Corleones are a sixth and smallest New York family, but were strong politically with Vitos connections in both the legitimate world and the underworld. TurnBull is right with how the movie made it seem like Corleone family was one of the Five Families. Michael had an airtight alibi, Connie knew what her brother had done. The members of the other families that switched over to the Corleones after the killings knew where the power lies and would need protection now. I do believe that a couple gave info to the Corleones on their bosses habits, Cuneo is the only one that comes to mind. Tattaglia was a creature of habit. Barzini was in and out of court, so they just waited, Stracci may have had someone tipped off the Corleones. The book and movie are different and creates confusion. In the book only Barzini and Tattaglia are killed.