When I did this part I sent Atton,Handmaiden,Bao Dur to the Tomb and all three of them where Dark Jedi so It was extremly easy. If I were you I would go back to a way early save right after you get your light saber and spend a lot of time with these Charecters to build your influnce and then offer to train them in the force. By the time you get back to that part you will Have three bad ass Jedi to Take the tomb and it should be much easier