There isnt interaction with your party members, and to complete their "quests" (if any) you dont have to have them in your party.
Anyway, i would recommend a whole party, or at least a 4 character party to the first time, Bg1 is hard

. Going solo, Ive completed it with a cleric/illusionist and with an elven fighter. It was pretty hard though.
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"TEEHEE !!!!" -
The Mighty CloudQueen, to Ertai