You can beat them even at Chapter 1 with 4 NPC. Just get near the mage, kill him in first round, set traps for thief and he'll leave the room and also his friends alone. And then, the rest is piece of cake..
Also it's possible to kill Kangax, guys in Twisted Rune in Chapter 2. The matter is a good strategy and luck of course!
-I killed Kangax in Chapter 2 but when I try again I can't kill him damn-
------------------
"A silent blade does not cut always best..
A tender touch from the heart may heal the wounds of my friends..
Or a song from the heart..
A duet with nymphs..
Forget 'bout nymphs, let's play KISS!!"
-Yngwie J. Amadeus Zoltan