stronghold CAN be done with 4-5 people.
3 guys need to stay behind with the informant with automatic weapons. one or two guys needs to leave the compound and head to the 3rd tower, back on the far left. using 50 caliber sniper rifles, eliminating the 6-8 guys around the tower will complete that objective.
meanwhile, the 3 guys with the informant must push him into the back room and hold the building at all cost while the two other guys finish off the other objectives.
one the third tower is captured, the 2 snipers can look all the way across the back of the map and see 3-4 vehicles parked, including an ADAT, LAV and an armored car. using the 50 caliber sniper rifles, you can blow them all up before they have a chance to attack.
once the vehicles are destroyed you can head over to tower 2 and eliminate the enemies. once this tower is cleared, a helicopter will appear. the 50 caliber sniper rifles can take down teh helicopter with a few shots.
once the chopper is down, take out the final tower. then, regroup at the stronghold, take out a few more enemies and GET TO DA CHOPPA'!
this map took me awhile to figure out, and once i did, it took 4-5 of us about 12 tries to do it. be sure to RELOAD EVERYTIME YOU SEE AN AMMO BOX. those 50 caliber sniper rifles dont hold much ammo, and are vital to taking down all the vehicles as quickly as possible.
also, if one of the snipers clearing the towers dies, it can be achieved by one. if both go down, one of the guys in the stronghold can leave and attempt to pick up where they died, but needs thier rifle. communications among players is always a must in this game, but especially on this map!