Hmmm... A Rogue/Sorcerer, Rogue, Duelist/Sorcerer and an undecided. Depending on the undecided player, it looks like you guys will be using alot of hit & run tactics, ambushes, and stealth. Unless the undecided player is making a Meat Sheild, heated melee combat is something this party should avoid like the plague. If nobody goes Cleric, hire one; you'll need him.
With two spellcasters, one of you should probably grab a few stock offensive spells and anything that will help you control the flow of battle. The various Wall spells are great for this. For ambush set-ups, nothing beats a good illusion.