I don't know if it's normal, but I actually passed this fight without a problem.
There is a bug (I think), if you talk to the chief and meanwhile your mate attack the other, you can keep talking to him and he doesn't fight, you got 1 of your character blocked in a chat with him, but with that you can kill all of them and then fight him, by the way the big worm don't spawn either, if the chief don't fight there is no worm, so you can kill the chief and the worm in a 1v4 XD
(sorry if i don't explain it well, i suck at english).
