What, they're already at it? Is it the point where Anomen and Kelsey duke it out in actual fight - as in, to the death?
If you can give me the actual dialogue, I might be able to help. In any case, try the Kelsey forum. By the way, my party went:
PC (straight fighter, no kit)
Jan (he's here for thiefy stuff)
Solaufien (doesn't act as a mage so much as a fighter with stoneskin and fireshields)
Kelsey (primary mage)
Anomen (healer and fighter both)
Jaheira (also healer and fighter; her fighting capability, of course, exceed Anomen's. Ironskin, baby, and not to mention her summoning spells.)
So my frontline: the PC, a heavily buffed Solaufien, Jaheira, and Anomen. I didn't bother with Imoen; I only took her along once and once only. She's an inadequate thief and, by the time I reach her, she's too low-level and her spell selections are pitiful.
I didn't do the sidequests; I've been through all of them already. But if I must chuck out someone, it's Jan.
