Sadly this happens during our pack meetings. It has gotten a little better with us. Being that you have actually handed out a paper saying what the rules are and they still will not follow them, then either you or the Cub Master might have to get up and stop the ceremony and warn the parents about the noise level and ask for some respect for the boys so they can enjoy their moment. Maybe remind them that #11 of the Cub Scout 12 core values is about respect.
Hope this helps,
Susan