Slight bump from someone else's almost necro
Was struggling with this too. None of the walkthroughs were specific enough on how to get the flamewalkers to have the dialog option about the play.
The reason was that the scripted event between Pyros and Venomin was not taking place. It did not take place until I went to the guard post. I probably could have gone to the fields of slaughter exit and walked south. All that I think needed to be done was to clear the fog of war from where Venomin was standing north of Pyros' domain. Once Venomin was viewable the land was restored between the north and Pyros' domain thus allowing Venomin to walk south to talk with Pyros. Till then the land was broken and Venomin couldn't be seen from Pyros' domain. However, it could be possible that it was intended for Lothar to be at the guard post on day 3 and the player talk to him there thus also triggering the scenes to take place.
So for day 3
Talk to Pyros at his domain
Talk to Lothar -- if Lothar is at his citadel then visit the guard post to get Venomin moving
Go back to Pyros domain
Watch the cutscene with Venomin
Wait a few and watch the cutscene with Lothar
Finally go ask about the play
From there I hope the rest of the walkthroughs are good enough...