Reviving old questions:

In the description of the peace conference, it is revealed that "When Michael had gone to meet Sollozzo, a Bocchicchio had been left with the Corleone Family as surety for Michael's safety."

Before meeting with Sollozzo, Michael asked Clemenza about the "hostage." Clemenza answer includes, "he is an important man in the Families."

If you subscribe to the theory that Puzo used "Families" as a collective term, then the Bocchicchios are included in it. And at least one of them is "important" in the underworld.