It's been a while, but I seem to recall that one of the familiars has a lock picking skill so get that instead of the rogue henchman. You need that big Barbarian as your henchman instead.
Use the Counterspell ability when facing spellcasters, you'll need maxed out Spellcraft and Concentration skills though. Basically, let the henchman do all the fighting while you blast from a distance and learn to run away. A lot.