You can group to complete this, though it is not a necessity.
You must be less than 15 levels apart from your group mates, or you will not get any credit or updates.
How to clear the zone and defeat Danak:
You only need to battle all sentient creature that can attack you. It is not necessary to kill the (non-aggro) tomes or to open the coffins in the zone. This includes the upper level, which is accessed by turning right in the first large room and heading upstairs.
When battling Danak, he will become immune to your attacks periodically. Click the colored glowies (similar in style to collectible shines) to damage him again. Just prepare for possible "adds" since an imp might spawn to help him.