An assasin wil probably be evil, so I would say:
Korgan, tank
Jaheira, mage spoiler and back-up tank
Edwin, best mage by far, don't bother with Imoen
Viconia, best cleric and very resistant to magic, plus with Str boost can tank.
The other slot you should leave for NPC,s to fill during their quests. If not try Haer Dalis. You dont really need another brick as both Viconia and Jaheira can double up with the right items. If you insist, go for Minsc or Valygar.
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Never accept an invitation from Wolfgir to a BBQ!