It's just you...technically.
You're playing 3 melee 1 caster against a current group of mobs who enjoy nothing more than spewing poison from their wounds and aoeing stuff with magic arrows/spells.
Firstly, your rogue is dex-based and can use marksman skills/special arrows etc... don't limit him by just using daggers (it only costs 2 action points to switch weapons in combat if needed).
Secondly, remember the rain spell. It'll put out the burning and limit fire, while also buffing cold spells (Jahan can use his chill spell for 3 aps on a guy who is wet to freeze them, great CC).
Knights might seem like great damage, but they have the lowest CC of anyone, so while you think you have more damage than other groups you have the worst possible control over the battlefield - I'd rethink your party make up if you're struggling.
