Make yourself King. (And disband the message group)
That does not make the group talk to more.
Doing something stupid is an efficient, if sometimes unpleasant, way to get people to talk more. 
While I just said general chattiness, I am hoping that its something general that actually is relevant and that the activity is persistent, not just a one-time thing.
If you can't get them to laugh with you, you can certainly get them to laugh at you. -_-
While lightening up the mood, with some comedy is probably a good idea, I don't think that will solve the problem completely nor I am exactly the best comedian. And yeah, I turned your suggestion into something a bit different.
Order them to talk! If they dont, get them fined/banned and they sure start to talk 
Fining could help though I am never going to ban someone over it, that's not option when your realm is at war and poor so those being fined would end up asking the lords for gold for the unit, ie the lords end up paying the fine.
