When the hero touches one of the NPCs you can make both of them say something. Like this.
Click/Tap on the actor that you want to start the conversation, then scroll down until you see “When Touched”. Then click/tap on that, then insert an action, and have one of the start saying things. Like this:
npc12345 says “Hello ther-”
npc09876 says “NO, STOP TALKING.”
npc12345 says “Why?”
npc09876 says “YOU JUST TALKED.”
And so on with whatever you want them to say.