So, I'm at the Cloakwood Mines and has run into Drasus and his party. Problem is - he's rather challenging and I can't seem to find a way to beat him. Even when I use the stinky cloud spell to temporarily disable the rest of his party he will completely obliterate me and my party on his own.

Am I too low level perhaps? Me and my party are all around lvl 4.

EDIT: So, I managed to beat Drasus directly after posting this, lol. But I could still use advice on the rest of the party. :)

Level 4 is enough for Cloakwood. It's more about equipment and tactics.

Since you're level 4 you won't have hold person yet, but what about using horror or web or entangle on top of your stinking cloud? He should fail at least one of those saves.
Wands or potions of fire can really soften up that kind of ambush, and you should have several potions of explosions or firebreath or whatever by now, plus wand of fire or two.
Wands of paralysis, fear and summoning are really useful too (frankly using wands is the main use for mages in BG since their own spells won't be that useful until the end).

If you really can't disable Drasus, do you have a dedicated tank with a good AC and hp (i.e. around -5 and 50 respectively) to grab his attention then let the rest of the party kill him, with ranged weapons if necessary?
If not (and you really should, there are several NPCs who can do this with the bracers of dexterity and decent armor), then you can just grab his attention with one character who can't use bows (the cleric or druid is fine) then run around while the rest of the party kills him with ranged weapons (yes, it's a cheesy but if all else fails...).

Yep, Stinking Cloud and Entangle, and use physical ranged attacks on the mages if they go invisible (arrows of biting from Taerom if possible), not spells. Keep your melee fighters out of the stinking cloud, and protecting your archers.