Barring drain, it's difficult. Nihilus' actualised power is almost impossible to tell, especially given his best feats were on Malachor which he could also potentially feed from...
Assuming he's, in this scenario, capable of what we've heard of him doing outside of drain, team one wins. Sion's bladework was impressive enough that Surik couldn't simply eviscerate him through his regeneration, so he should be able to hold off Maul or even win via attrition given his literally immediate resurrection abilities.
Traya can take Dooku, especially on Malachor. Nihilus and Vader is close, but Maul is easily the weak link so I expect team two to fall that way. Traya or Nihilus can take Maul out of the picture with even the slightest opening, and from there the fight is over...