In Julius Caesar, Act V, which four characters finally confront one another in scene one of this act?

Having spent the majority of Act IV engaged in military
tactics and strategy to prepare for the war that is to come, Act V scene 1 takes us
directly to Philippi where, according to Brutus' plans, his armies have marched out to
meet the forces of Antony and Octavius. It is thus at the beginning of this final Act,
which is crammed full of so many different kinds of action, that Octavius and Antony
meet their enemies, Brutus and Cassius. The leaders meet to exchange "Words before
blows" in the words of Brutus, and exchange insults and mock each other. In particular,
Antony insults Brutus and Cassius over their hypocritical attitude towards
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, behind

Struck Caesar on the neck. O you
flatterers!

Having spent some
time issuing challenges to each other and insulting each other, Octavius and Antony
leave the field to ready themselves for battle.