You have two archers, and you can find acid arrows and fire arrows in the first level of Dragon's Eye -- acid arrows and fire arrows will kill off the trolls, but don't waste them. Use ordinary weapons/arrows until the trolls fall, then switch to your acid/fire arrows and finish the troll who falls with just one arrow (it's all it takes).

I'd restart the game with a proper party.

You're not screwed, but the game's going to be pretty tough. As Hickory noted, you can get fire and acid arrows. Be aware that the fire damage from the fire arrows is applied as a magical effect, so sometimes the trolls save against magic and they have no effect. Acid arrows don't seem to work this way and seem to finish them off 100% of the time.

There is also a sword available at Conlan's smithy that deals fire damage, which will finish off trolls. I believe it's actually called 'Trollkiller'.

As for the spiders, you need magical weapons to damage Wraith Spiders so make sure you're using enchanted weapons on them. Other spiders can be killed with regular weapons.

If you're determined to go with a more balanced party, there's no need to restart. Simply figure out which character(s) you want to drop and give their gear to one of the characters you're going to keep. Save your game. Start the game again and when the screen that shows your party pops up, delete the characters you don't want. Roll up new characters to take their place and then continue to start the game. The new ones will be first level, but they'll level quickly. If you want to get them up to your party's current level right away, simply use the console to give them XPs. If you need advice on how to do this, just ask.

If you had a mage, then the level 2 spell Melf's acid arrow, or the level 3 spell flame arrow will finish off the trolls.

Use these when you run out of arrows.

I'd also restart with a more balanced party.

you can create a new party member (taking out one of your previos) as you are alreaady lvl 6, the new PC will levelup fast . Other option is beginning to consider to multiclass to sorceres,wizard, druid or cleric some of yours PCs.

If you create a new PC , try to return to a previous clean area and begin to rest a lot for increases his stat.

An option I considered suggesting, but it requires the proper ability scores in order to do so. To wit:

17+ INT to dual class to Wizard
17+ WIS and 17+ CHA to dual class to Druid
17+ WIS to dual class to Cleric

Sorcerer is not a class in IWD1, so that's out.

As well, the characters must be Human to dual class. Since there are so many variables, I figured it was pretty much pointless to suggest dual classing in the first place.

My fault, I was thinking about IW2 instead of IW1.

Thanks for the tips all. I found the fire/acid arrows and am slowly making progress without having to resort to changing the composition of my party.