There are 2 very important things to remember in BG II. The first is having the right eq for the right job. If you are hell bent on doing the fight and you don't have alot of eq to try out then this isn't gunna help much.
The second thing to remember is magic rules in BG II. I would suggest you summon up some cannon foder. Really I suggest you use summon spells all the time. Since your main is a cleric plus you have jaihera you should have plenty of spell slots left over for a nice pack of summoned creatures. Druids are great for summoning stuff. I am not sure what levels your characters are (I assume pretty low as you just got the game) so the monsters you can summon will not kill the troll right out for you but don't be afraid to summon skeletons or elementals and have them take the hits while you hit the bad guys from a distance. Or send the summoned creatures in first and get the bad guys aggressive to them and then send in the warriors. A group of summoned monsters (you can summon a max of 5) plus your own party with haste cast on it(haste is huge and SOO efective when you cast it after summoning creatures) should be able to take on any pesky little trolls
also for your cleric you may want to try the flame blade spell (level 2) for killing trolls.