Federal law requires that there be a seat belt in every designated passenger position, so if your coach claims to accommodate for use 6 people, it must have 6 belts installed. But individual state laws determine which passengers must actually be wearing a seat belt when under way. And the laws for passenger cars may or may not apply to large vehicle, so check the laws of the state you are in. And like speed limits, seat belt laws are not reciprocal - you must obey the law of the state your are currently in, not just your home state laws.
Former owner of 2004 American Tradition and several other RVs
Home is West Palm Beach, FL