The "triple tow law" is called a Recreational Double here in Michigan. We are one of the states that allow it. The operator is required to possess a Class A CDL license with Doubles/Triples endorsement, or they can take a test and add a "R" endorsement to a normal passenger vehicle license.
There are states that don't allow this type of towing situation, however, I believe most of them will let you go if you are properly licensed and plated from a state that does allow it. They may ,of course, stop you to check all that legalization. So just make sure Momma puts her margarita down between the seats in those states.....