We will kill all conspirators! What is your name?
Antony has just gave his speech at Caesar's funeral and turned all the people against Brutus and the conspirators. The people of Rome are now on a man hunt for the conspirators planning to kill all them.
The towns people think Cinna the poet is Cinna the conspirator so without hesitation they decide to kill the innocent Cinna the poet. This shows how serious they are on killing all the conspirators.
The towns people have now murdered Cinna the poet and they are still hunting down the rest of the conspirators, they will stop at nothing.
Mark Antony is saying that all conspirators must die even if the are family and unfortunately Lepidus' brother, Publius, is a conspirator. Octavious must ask for consent because if they kill Publius without telling Lepidus before hand he could get angry.