Find a Queen Wasp. Look for the zombies that are either holding their head or looking at there arms slightly above their heads. Then, get the katana from outside the first window on the back wall of the Colombian Roastmasters. Use the Wasp to kill most of the zombies. The best place to get them is to run for the middle. You might get shot once or twice, but if you have the queen ready this is less likely. He will hit you with a shot from the rifle. Run as fast as possible upstairs. Brad will get hurt a few times; just make sure he does not die. Run to Carlito and slice him with the katana. Be careful -- he tosses grenades as he is running and will hit you with the rifle after you hit him once. This also works with the hammer, but it is slow and he will hit you before you can hit him.
When fighting Carlito the second time with Brad in Entrance Plaza, it can be quite difficult. The best sniping position to kill him from is in the pink shop directly above the escalators where you first come in. There is a table with some signs on it. Position yourself between the little signs and shoot him with the rifle. Carlito may also turn his back to see where you are shooting him from.
To easily defeat Carlito the second time when he has a sniper rifle, begin by running up the stairs. As soon as you get up, turn left. Keep moving to avoid his shots. Try to stay out of his sight. At the "corner" on the second level near Carlito is a sporting goods store. Go inside and grab a hockey stick or two. Leave the store and quickly run across to the pillar. Stand almost even with the pillar so that Carlito cannot see you at all, but will keep shooting at you, only to hit the pillar. Hold RT to aim with the hockey stick. The end of the stick (and therefore the puck) should be sticking out past the pillar while your body is still fully protected behind the pillar. If not, reposition yourself until you can shoot pucks at him. Once set, start slapping away until he "dies" and the intermission sequence starts. Be careful not to also hit Brad.
The third time you fight Carlito is when collecting the bombs in Case 7-2. To kill him easily, unlock the Real Mega Buster and shoot him about three times when he appears. Additionally, if you want to have a safer trip during the mission, instead of entering the tunnels through the parking lot with the motorcycle, get the maintenance key before the case and enter through Paradise Plaza. There will be a white sedan that will not break down as easily as the motorcycle.
