how is the argument between brutus and cassius different from the one between octavious and antony in scene 1

I think you mean Act 5. I'm assuming you mean scene 1 of Act 5, where Octavius and Antony are arguing about battle strategies, then later in the scene, Brutus and Cassius are discussing what will happen if they are defeated?

If that is the case, then there are definitely differences as I mentioned above. Octavius and Antony are butting heads over not just who should take which flank of the battle, but more importantly, who is truly in charge of this triumvirate and their army. Octavius, as Julius Caesar's heir, does not think he should take orders from Antony, and so we can see that this idea of a 3-man rule of Rome (Lepidus isn't even around anymore) just isn't going to work. Octavius refuses to listen to Antony's strategies, and so there is some heated "discussion" happening here.

Brutus and Cassius, on the other hand, aren't really arguing, but rather determining what they will do if they are defeated by Octavius and Antony. Brutus had formerly condemned his father-in-law's suicide (Cato), who killed himself to avoid having to submit to Julius Caesar. Cassius is questioning Brutus as to whether he is willing to submit to Octavius' authority in the same situation, and Brutus replies that no, he understands now why Cato did what he did, and he plans to follow the same path if the battle goes against them.