1. Who was responsible for all those of the deaths?

In part II he was like Crucifixio's (aka. Cross) right hand man... Billy..He thought that if he just killed off Cross (which he failed) and oh i forgot that guys name the one that was real close to cross the one that his family was killed in the church in sicily. and the sons, he would be able to obtain power...
2. How many Crime Families were attacking the Clericuzio?

In part II if im correct, it was Billy and his people trying to take over the clericuzio Family.