You can kill everything outside from the top level with arrows and spells. First kill all the sleeping folks up top and the dude reading out on the point without aggroing everyone below - Hide - sneak to edge overlooking camp below - fire arrow/cast spell - walk back from edge a bit - hide. I take down the archers and spell casters first, after they're gone you really don't need to bother hiding anymore. Inside obviously you can take out everyone but the leaders one group at a time before starting on them if you're careful.
