Request for improvement...
Generally, the difficulty of the CoC encounter varies according to the party composition, the Protagonist's level, the game difficulty setting and of course the tactical skills of the player. Some players find the encounter very hard while others breeze through it without problems. I'm fine with that, since my goal was to create an interesting party vs. party encounter where opponents fight fair and have no extra advantages over the player's party in terms of resistances, immunities, hit points, attribute scores, spells, special abilities etc.
Maybe give sorceress a scrol of True Seeing?
I suppose I could do that, however, it should be noted that all spells which opponents cast from scrolls can be disrupted by damage and Miscast Magic effects in RR. This behavior is contrary to the unmodded game, but it is consistent with PnP rules.
Because two other thiefs didn't seem to detect illusions (as described in documentation) at all. Well, maybe they were too busy drinkig potion of healing or whatever...
That's a possibility since their AI tends to prioritize defense over offense when they are badly hurt. Furthermore, it should be noted that Venduris' Detect Illusions ability is enhanced due to his background and special training. The other CoC members use the regular Detect Illusions skill and, just like PC Thieves, they must make the necessary skill checks in order to successfully dispel illusions.