What I need is, after initiating dialogue with an npc, said npc and all npc's in the room attack the player.
Ah yes, we're working on something very similar! SetRelationshipRank will do the trick for you:
http://www.creationkit.com/Actor.SetRelationshipRank_%28Papyrus%29
What I did is set a quest stage via the fragment in the last dialog where you want them to become hostile, and in my quest stage use:
Alias_MyActor01.SetRelationshipRank(Game.GetPlayer(), -4)
Alias_MyActor02.SetRelationshipRank(Game.GetPlayer(), -4)
Alias_MyActor03.SetRelationshipRank(Game.GetPlayer(), -4)
and so on rinse/repeat for each of your NPC's.
There may be a way to do it by creating a faction and making them friendly to that faction, and then removing that in your fragment, but I haven't done it that way yet.
For the shout, I would use a force greet package that becomes valid when you defeat your King. When he force greets you, you can run through the teaching of the shout in your dialog branches. You could also interrupt your dialog with a short scene where he walks to a central area and demonstrates the shout, then comes back to talk to you. Scenes are wicked cool! Give me a little more detail and I'll try to help more!