So it seems we kinda settled on what to try first - but there isn't any indication on the how. We would be attempting to remove a target from the middle of the enemy encampment, and I feel like I can't gloss over that part easily.
I realize the fault lies with me, as the options seem like stand-alone choices, but they aren't - at least not to that extent. Well, there also are some questions and inconsistencies, so I'll answer / address those first.
Could we also "create" a shadow ogre as a bodyguard as well so that we seem even more intimidating?
These people are probably chivalrous and couldn't attempt any risky maneuvers for this precious thing they call "life".
As mentioned in the first and second option, we can either cloak ourselves in an illusion, or spawn a separate one nearby. Both will dissipate once we get too close to the fire though.
Us taking a hostage, means that we are likely to convert it. Unless it is a loved one, or someone of great importance, they aren't unlikely to give up on an innocent, lest the later becomes a monster.
When they see us running away, (and they will, once we're far enough.) the trolls inside the cave will be able to strike.
The Pyre - and thus the Priestess, too, is in the middle of their camp. They will see us coming at them, long before we even get to run away - though then, they are bound to loose us in the dark.
The trolls inside the cave, are still boxed in by half of the host - if they haven't already fled towards the caverns, that is.