the problem with this mission is the fact that one of the snipers is the team leader. consequently, you can't order him to hold fire at all.
now, unless you do that switch weapons thing someone suggested above, you have to remain in control of the team leader for the time being.
this means that you have to provide sniper cover yourself. so simply set up your team on the ridge while holding fire. once ready, order everyone to open fire and target the important enemies yourself (the officer, the drivers, everyone that tries to use the radio).
now to teamswitching. only teamswitch once all enemies in the vicinity are dead. this will probably inculde the reinforcements as you might not be able to prevent their arrival.
when all seems clear, teamswitch to your saboteur, enter the camp carefully as there might still be a few soldiers alive, blow the vehicles and get the hell out.
you'll probably not be able to reach the extraction point with your complete team as you can't give orders as the saboteur, and the team won't respond anymore when you switch back to the team leader (the second sniper probably will, but the saboteur won't).
it doesn't matter, though, just reach the chopper and it's all good. i hope that covered everything.