My worst flight experience - American Airlines assigned much smaller plane to the flight from Charlotte to Roanoke compared to tickets sold

Today I was traveling with my wife and 3 kids from San Francisco to Roanoke with connecting flight in Charlotte, to our surprise American Airlines employee has closed the gate's door right before us and told that us that the plane is full and we cannot board this flight despite the fact that I've checked in earlier today with all the seats assigned. What made the things more odd was that later they've allowed to board 6 more people that were staying behind us and probably actively negotiating something behind the scenes.
Apparently AA has assigned smaller plane to this flight so they couldn't board around 16 people with tickets. It was weird experience watching how the smiles have gone from AA employees faces when they've realized there is an issue with the plane and immediately they became very rude with passengers. I've started filming they behavior on my phone, one guy has rushed to me and told that it's prohibited to filming them at the gate and forced me to delete what I filmed threatening with calling a police and having me arrested.
So now I'm writing in the corner of the hotel room (not to a surprise - the room we've got is too small to accommodate 5 people) with slight hope to get to our destination tomorrow - we were told we can try 11am flight to Roanoke tomorrow if we get early enough to the airport - looks like regularly ticketed passengers take priority, I don't know what would happen if we take seats of somebody who has purchased tickets but late to the airport.
Hope somebody at AA will read this and take some measures the future passengers will be treated with more respect, or I we will witness this company goes bankrupt.
And also do you know if it's really prohibited to film videos/take pictures at the gates at airports?