Absolutely. If they are still hangin with Mom, they'd better respect her wishes. Sitting down together for a meal is extremely important for families to do... to connect, regroup, share a meal, communicate... just out of respect....

You actually serve a meal and they don't come? 

My answer would be completely contingent on WHAT they were doing not so much whether it was ilegal or not. If someone was acting out against others in some way, it would be more likely I might turn them in

You can do anything you want but is it in the best interest of your daughter might be the better question to ask. "sex offender" can mean a lot different offenses but personally I wouldn't think I would want to put my daughter or my custody of her at risk, do you?