[QUOTE=Klorox]What would you make the protagonist in this party:
Aerie
Jaheira
Jan
Imoen (not multiclassed, but she
is your "sister")
unknown (maybe nobody)
Thanks in advance.

[/QUOTE]
Lets see...
- 3 Mages (Aerie, Jan, Imoen)
- 2 Thieves (Jan, Imoen)
- 2 Cleric/Druid (Jaheira, Aerie)
- 1 Tank (Jaheira)
Ok.. so you need a tank as a protagonist, that's for sure. You won't need extra thieving skills or mage spells, because you already have 2 thieves and 3 mages. You also have one druid and one cleric (Except that Jaheira won't be casting spells alot if she's your only frontliner).
So, yea, you really need a tank. It can be a fighter/mage, a fighter/druid, a fighter/cleric, a ranger/cleric, a fighter/mage/cleric, a fighter/mage/thief or even a fighter/thief. You could also want a support character like a Bard (Blade, Skald, Jester?) or a Paladin/Ranger. You could also try a monk if you haven't. Nice frontliner.
Well... you have alot of chocie.
P.S. You SK Imoen in a multiclassed char instead of a dualclassed one.