Yep I had problems too and then I cracked it. Use Tharan, force lift the Sith Sorcerer to keep him out of the game and keep smashing at the other guy. Avoid any AOE attacks. Heal before the other sith drops. It was actually shockingly easy once I got Tharan involved and I did it first go. However, I did spend a shedload buying Tharan some top gear first from GTN. Worth it as this was the only part of the game that has had me swearing out loud!