From xenowiki

From a hunter's perspective...

You have Dorothy, Toto, Lion, Tinman, and after they're all gone, the Witch spawns with her tornado. I don't remember what the game calls them, but you'll know which is which.

From what I can tell, there may be a certain order to kill them, but I don't know it. I just kill them in the order that the raid leader says. :)

Looks like a tank-n-spank to me with the exception of the Tinman who seems to be kited and ends up being last to be killed. Once they're all dead the Witch will spawn. Avoid her tornado and dps her down.