You don't need such a big team to clear Sector B actually, did it alone myself.
Had a M249 before, but ammo went empty so fast, because that bots can take as much as Patient Zero/Doctor Ivan.
Then switched to a Pecheneg+Nightvision (because it got dark) and it only needed like 10 headshots to kill one.
Actually we was 3 when moving there, but, everyone who plays with me dies, except me, I always live.