There should be one or two guys patrolling that area that you should be able to take out with silent weapons.
As for the big group: grenades are your friend! Use Selma’s Tree Hugger to pin them down, then throw grenades and Molotov cocktails to set them on fire and do a lot of damage. Don’t forget about the Medbot though, as it has a tendency to spring to life and revive dead comrades.