The 3 best characters to take are Mandalore, Atton and T3-M4. !Remember to save just as the fight begins! Be T3 and try to make Atton die at the very end of the "Swimming pool" where the sith lords are, and just let Mandalore die wherever you want. Continuously run as T3 around the pool so the sith are chasing you, and every time you pass Atton, he will come back to life and distract the sith, so you have time to equip the droid shock arm and the droid flame thrower. Keep using the droid shock arm on them and keep running around the pool so that Atton kjeeps waking up. Every time you kill one of the 3 sith, save game. Good luck!