Ok, this is a run we did in Shadow Labs under the normal difficulty. The party people were:
Stibe, Kara, YingYang, Punana, Myself. 2 rogues, 3 druids. We managed to skip some mobs...

...as you can plainly see...

..But unfortunately we found out, or better said, remembered that these Overseers have the Fear spell. Ouch.

And we got passed the second boss, just to reach the third and find out that...

Behind Vorpil there is another door that won't open unless you kill him - Killing him implying clearing the whole room.

you got mail