True this is one side of the story. The other parts are they were questioned by the FBI for less than five minutes, issued an apology by the airline and put on the next available flight. That leads me to believe this was more of an over-reaction by the crew than the family being out of line. Plus this is not the first time a United crew has been in the news recently for over-reacting.
I hate to throw flight attendants under the bus, but my guess is the flight attendants made a much bigger deal over this than it really was. The only information the captain has is via the flight attendants, so if the flight attendants are not accurate in their portrayal of the events, or are over reacting, the captain has no way of really independently verifying what is happening.
That being said, the family needs to chill out a bit about movies. Americans are way too uptight.