Brutus- selfish, low self-esteem, not very educated military wise.
Cassius- He likes to look out for people. He worries badly for his friends like Titinius and Brutus. He is much wiser than Brutus and knows he has a doubt about winning the battle. He is taking every procaution so that he wins the battle, which Brutus just wants to fight and not thought out wisely about what he is doing. Cassius is wisely planning it out.
Brutus- He wants to kill himself because he does not want to lose his honor by being killed by someone else, which to me is selfish. He has a low self-esteem because he feels he lost the battle. Brutus's troops were advancing unevely and without the support and he sends a message to Cassius's troops since he thought Octavius's army was approaching too quickly. This shows he is not strategically capable of military strategy.