In which ways does the identification of people to be killed in Act IV, Scene 1, of Julius Caesar affect the audience?

The cold-blooded manner in which Marc Antony discusses the elimination of political enemies is disturbing and ironic to audiences.

In Act IV, Scene 1, Rome is in crisis and on the brink of civil war, as Antony has predicted. Now the new triumvirate of Marc Antony, Octavius, and Lepidus is on the plains of Philippi where they will soon battle the forces of Brutus and Cassius. In this scene, however, Marc Antony and Octavius focus on their plan to eliminate their political enemies and steal legacies from other Romans.

As Marc Antony speaks with Lepidus, they go down the list of names marked for death, and Lepidus agrees to the death of his brother; Octavius asks Antony about another name, and Antony agrees to the death of his nephew. Then, Lepidus is sent to procure the will of Caesar so they are able to view some of the legacies given to the citizens and reduce them. 

After Lepidus departs, Antony treacherously remarks to Octavius that Lepidus is a "slight unmeritable man" and undeserving of sharing the triumvirate with them. Octavius argues that Lepidus is a "tried and valiant soldier," but Marc Antony's cold opinion of Lepidus as no more than his horse is disturbing. Further, he tells Octavius he has already sealed the fate of Lepidus with his mark.

These words and actions of the triumvirate, and especially those of Marc Antony are ironic because, in Act III, Antony was the one in Act III who questioned the honor of Brutus and the others who assassinated Caesar, concerned that they would become tyrannical. Now, however, it is Antony who has become tyrannical instead. Also, in Act III Antony has addressed the plebeians as inheritors of Caesar's wealth, but now he has their legacies taken from them or reduced. Ironically, too, the devious planning of the death of Lepidus and the civil disorder caused by Marc Antony and the others is much worse than Brutus's fears of Caesar.