Okay, so I'm in the second co-op mission. I'm not quite sure what section of it is, but it's where you have to find the blueprints and you hear about some red mercury. It's after the gun turret/fan part. Anyway...
I got the first two sets of blueprints and as I go back through the hallway towards the elevator we keep getting stuck in there. We can't kill both[or all three] of the guys on the other side of the elevator. How is the best way to get through there?

Please help.