Im pretty sure we have all the origin characters already in game, Minsc to fill the ranger slot, and Karlach probably dark paladin of some leadership flavor or possibly even a bard by her clothes using her songs to boost her troops in hell, with the werewolf as a shapeshifting druid.
That leaves, sorceror, monk, barbarian, and one other as PC only classes; unless Minsc had a change of heart and converted to Barbarian or Monk.
Paladin (or even blackguard) is unlikely for Karlach; paladin subclasses almost never use ranged weapons.
