This module is written for 6 players, but is far too easy or that, unless the players are new at pathfinder.
One way to remedy this would be to...
Spoiler:
-remove the assassin levels from the boss, and put it in something else (class levels in cleric, for instance).
-change the bbeg's tactics. Summoning is a waste of time if the chance that it will be succesful is not that high.
