Maybe they're finding it tough, too, to break a bad habit. Not as a punishment but as a time for reflection for them, can you send them to a different part of the house with a pen and notebook in hand and have them right down what is "eating them" and then write something positive to replace the negativity?

That way, you get them out of your hair, you don't have to listen to them and it helps them to break the cycle, too. What do you think? Might it work?