Kivan and arrows of detonation (after the dispells suggested by @SirBatince).
One thing you will find useful if you can still get it, Wand of Monster Summoning. Secret of Sarevok IMO is never to go anywhere near him, that sword is very, very big. Let him waste his time killing the summons.
Your levels are more than suffucient, at this point, I don't know how much grinding will actually help you. Potions are incredibly helpful, as has been said, your party composition is pretty good. I think you just need to get your tactics down. Watch what the enemies do and where they appear, make note of traps, etc. Because of the relatively low level cap, BG1's final fight is significantly harder than BG2's. Don't give up.
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People will be able to give more specific advice if you describe your party.
Minsk 6
Imoen 7
Kivan 5
Dynaheir 7
Dwarven cleric 6/6
however you can import whoever you want.
as for Sarevok fight, use Arrows of Dispel on him and his 3 goons. makes a serious difference at little cost.
Kivan and arrows of detonation (after the dispells suggested by @SirBatince).
One thing you will find useful if you can still get it, Wand of Monster Summoning. Secret of Sarevok IMO is never to go anywhere near him, that sword is very, very big. Let him waste his time killing the summons.