first of all Charisma is a waste of time because once you get into the third act, its all over the place, better weapons than you can imagine..
Sorcoress is easily the best character in the game, give her the meteor, ball lightning and fire circle spells and she frickin\' rawks over everyone. Also make sure your bro buys strength rings so he can carry plenty of stuff later on (it comes in handy)
its a pity the archer is crap (sorry pahn

)
also with the Dwarf you really should go for an axe/warhammer that way you can use his magic attacks which come in handy (how often do you use the shied anyway?)
also.. good to see your on Act 2 and already with Full Plate armor

p.s. the sorcoress looks better once you take her armor off (she has a thong!)