Okay a few ideas to keep them quiet, might not be perfect but hope it works;
Put a TV in the cook house, MTV, Simpsons, Futureama can keep the "kids" entertained and quiet.
Run a Quiz, they need to be quiet to hear you read out questions, and then the individual/ team etc to win gets a prize, like no stag/ guard house duty, lay in, run ashore etc etc. Or the loosing team gets stag, extra duties and so on, so they want to listen and win, therefore are quiet.
If they are seroiously arsing about, scary RSM type present will put them back in check.
Hope something works out and the kids behave, if not send the RSM in with the RPs and then they can resolve it as they know best.
Either that, or explain why they cant chat while they eat their meal. If its got to the stage where their dancing on the tables or conducting gang warfare during dinner, you've probably lost some control.