I that case, you have a pretty tough way in front of you. You will have to sneak arround and explore a lot, until you got a level high enough for decent skills. But even then not sure how much cheese will be needed for the fights, it is really tough to get bast all those armors. Archer will probably need scoundrel as well for more armor penetrating skills. Mobility skills will be important aswell. For high damage output two mages are perhaps the best, just let everything explode with fire & poison, and stun or freeze them, after magic armor melted away. or perhaps pure physical with archer and tank, using mage mainly for support (more armor, haste, heal, teleport, etc.)
The game is more 'planned' for four people parties and the balancing is pretty off still because of Alpha anyway.