what i do is sneak a thief like imoen up to just where i can see one of them , then back off, and shoot an arrow. this splits their party. if you can lure away enough of them before the dialogue comes up, they remain neutral, and wont attack. use dire charm, if you can, then walk them to where you can kill them easy with a backstab to start it all off. use arrow of dispell on the mages. invis with the AI off walk right up to the archer, forcing him to use melee weapons. you score some nice arrows then.
and yes, cloudkill/stinkers work great with a cleric entangle.