I made a video tutorial for implementing a dialog with multiple NPCs. It was suggested I put it here in the guides section, which makes sense.
Relevant time codes: -Adding NPCs to dialog editor - 2:34 -Why you can't just add multiple NPCs through the dialog editor and leave it be - 6:46 -The little bit of scripting you need - 8:58 -Set the dialog to start on trigger instead of on clicking NPC - 11:22 -Regions in story editor (I just think they're neat!) - 13:58