This is a arguement people have had for years.
NcCole Treadway

Which is exactly why private citizens like your nephew are free to fly that flag on their property. The national government can reasonably restrict the states that seceded from flying the flag as a public action. They were treasonous actors and murdered innocent US soldiers, then they were defeated and were allowed back into the union (eventually) with full political privileges. Advocating or celebrating that act of treason from a local or state level is not one of those privileges.