After the first boss, if your party has a stealth class, you can stealth to the next area where the mob would jump down to kill all of the big zealot guys. While he wont spawn unless you kill the 2nd boss, a portal would appear at the beginning of the instance so you can have your group teleport out/teleport back in to jump to the 3rd boss. Only downside is that unless you do it right, the patrolling mobs can see stealth and will kill you. Just try to get to the next part before dying.
3rd boss is also skippable but that's probably common sense.
Sorry I'm bad with names but if you guys have any questions or need clarification I will be happy to help.