Take people out from the tower, you may need to swap to your pistol for the guy in the middle of the town if you're using a high powered rifle as the enemy will hear any bullet penetration. Have your team take out the guys in the woods on the right. Shoot the guy in the tower in back of town, the guy in the tower to the left of town, the guy at the base of that tower. The move along the dock-type area, take out the central guy (the guy I used a pistol on), then the guy to the right side of that dock area, and finally a guy to the back right. Chances are you will only be able to see the guy at the back right's flashlight. From there head through the drain pipe to the front right of you while you're in the tower looking at the town. Wait at the other end for the truck to appear, then target the group of enemies that move toward the center of town (3) and the guy standing behind a barrier at the center of town. Wait until a guy comes down the hill from the barn and he will stop and turn right to patrol away. Once he starts moving away, take the 4th truck guy out, he'll be at the back of the truck. Then help your team take out the 4 guys at the center of town. Now follow the guy who came out of the barn and take him out. Head into the barn and take out the guy who is patrolling the top area by shooting him from below. Climb the ladder and look out the window that overlooks the area opposite the way you came in to see a guy that should now be moving toward the barn. Kill him. Now look out the window that is facing the tower you were in earlier to find and kill the last guy. This just worked for me, hopefully it does for you
ANYWAY, now I can complain. I made it all the way to this area and I had two challenges to complete, the neck snap and pistol ones, which I completed and then died and reset. Once I respawned at the checkpoint I noticed my 3 double kill and my swamp man challenges were no longer checked, even though the double kill one was 3/3 and I'm 100000% positive the stealth one unlocked. After the breach and clear my swamp man one even became a failure, which is hilarious since the helicopter is supposed to appear..... I made it through the whole goddamn mission without getting spotted and I still lost a challenge that I already completed. Luckily I unlocked the double kill one during the breach (making it 4/3 -.-).