This is why I put any important text in boss speeches. Any original NPC you add to the story can be a 'boss' also. Boss speeches have several advantages. One, they don't fire until the boss is attacked. They can be made sequential. And they're available to be read by any player on the team, and not just the leader. It's also the simplest way too add text; each original character in your design gets a speech where they explain who they are and why they're here. If they have NPC dialog in a tab every player gets to see them if interested.