1.
Killer. He is the second strongest of Kidd who was among the strongest Supernovas along with Luffy and X Drake, so his right hand man Killer who was a Supernova as well should win this group, though I do believe that Brook can put quite a match, especially due to his DF ability that makes him practically immortal unless you desintegrate his bones and that's close to impossible if you don't know it from the beginig.
So Brook might have a chance for surprise attack, when Killer thinks that everything is over.
And Brook has as well his musical abilities that are fearsome as well.
2.
Brook. He is the second one who should advance to the next round. He is obviously way stronger than Absalom. There is no challenge in such a fight.