Can anybody help me? I've got 2 POW's, but they are just sitting in any ally, and I don't know what to do next. Is there a 3rd POW? If so, where is he, because I've searched everywhere I can think of.

Not played for awhile but make sure everywhere is safe (such as no enemies can jump out and attack) Also head towards your destination and make sure you are using the "follow me" command

when you have free both of the POW's , they go to the alley and wait for you. you then have to go back to the very start of the level making sure that none of them die.
once you walk past them (the POW's)follow you in the direction of the start of the level (taking a short cut instead of walking all the way round. along the way back there are snipers in the lookout posts in the compound shooting out to the open ground you have to cross. you need to position foley in a well covered spot so he can take them out as soon as they appear. then there are also 3-4 waiting on top of the bridge at the very start of the level, so make sure you have 2 of your team (i use bradley to follow jones) with foley and connors following behind the pow's (change foley to pistol once he has taken the snipers out)

Good Luck