1. If you viewed that scene, how did you miss the follow-up scene when Michael very explicitly tells Tom that he is not a wartime Consigliere? If you somehow missed that scene, there is an immediate subsequent scene where Vito tells Tom that he must not have any part in what is about to take place.

2. Accuse Pentangeli of what? Nothing. Instead, he tells him with an irate demeanor that his attempted assassination took place in his home, etc. Since Pentangeli is in charge of the Corleone family activities in NY, why wouldn't he utilize Pentangeli to take his revenge?

3. It's the Rosa[t]o brothers. Here again, there are prior and post scenes that make it pretty plain that Hymen Roth wants Mike out of the way, that Pentangeli is Mike's ally, and that the Rosato brothers are Roth's allies.