I retired recently, before that I traveled extensively throughout my career, Asia, Europe, West Coast mainly. I would say that I am a traveling pro and as such I have gotten to know many Flight Attendants, Booking personnel and Pilots. They have extremely difficult, "dealing with the public" jobs and often times passengers go out of their way to make their difficult jobs insanely difficult. My heart lies with the crews honestly. With that said, and speaking as a father of a 27 year old Special Needs adult, and after reviewing the short story above, the fault in this case lies with one person - read on.
The first major mistake was made by the Booking Agent. The booking agent should have figured almost immediately that changes to the seating arrangements needed to be made, seeking out volunteers way before the flight boarded. Believe me, there would be many volunteers who would move their seats if the Booking Agent explained the situation on a volunteer basis. I was approached recently to change seats for a Cancer patient/relative. No problem. People are generally reasonable.
Failing that first critical filter, the Flight Attendant totally failed and made thing super worse, embarrassing the family and creating needless panic among the Special Needs Adult. People with special needs generally cannot deal with change. Hell, many "normal travelers" go insane because of travel pressures. It isn't a fun process for anyone. Imagine the angst and surrounding vibes of the nervous travelers that Special Needs adult felt?
Flight Attendants, generally speaking, don't get paid until the door closes, i.e. until all passengers and baggage are stowed. The terrible feeling the family was going through after "Airlines Systems #1" failure was acute... I've been there, it sucks. Only to be confronted by "Airlines Systems #2" failure... and finally, the Pilot (Airlines System #3), who was probably making political points (union or otherwise) by supporting #2... was the coup de grace. Giving the Pilot the benefit of the doubt here, perhaps the Pilot was reacting to the Special Needs adult screaming or having a panic attack. It is common and if I were the pilot, I would have to move the passenger off the plane too. Not sure if this happened or not.
Who is at fault here? The Exec who is in charge of the Airline's systems. The Airlines COO should be spanked for not thinking of this common contingency especially with the explosion of Anxiety and Autism our society. With systems comes employee training and someone within the employee chain #1 - #3 would have solved the issue prior to boarding if the system was in place. Not unlike making special boarding provisions for "people who need extra help or people with young children".
Poor Family, Poor fellow passengers, Stupid COO.