Antony and Octavius do not meet with Brutus and Cassius in a tent. They are on the battlefield itself and have a meeting out in front of their two opposing armies.
They stand, and would have parley.
Stand fast, Titinius. We must out and talk.
Shakespeare could not stage a battle between two large armies on his little stage. Characteristically, he relies on dialogue, which is his forte. Nothing much transpires at the meeting of these four men, but it enables Shakespeare to bring them all together for the only time in which all four will appear together in the play. They have a battle of words as a substitute for showing a battle between two mighty armies. Brutus says, "Words before blows: is it so, countrymen." He seems to be hoping that they can arrive at a peaceful solution of their differences by reminding them that they are fellow countrymen and by opening the parley in a friendly manner. But Octavius and Antony are both too angry to talk of peace. Antony destroys all such possibility by saying:
Villains, you did not so when your vile daggers
Hacked one another in the sides of Caesar.
You showed your teeth like apes, and fawned like hounds,
And bowed like bondmen, kissing Caesar's feet,
Whilst damned Casca, like a cur, behiind,
Struck Caesar on the neck. O you flatterers!
(Act V, Scene 1)
And their return to their respective armies to begin the battle.