This entire article leads you to believe that the family is the victim here. And then the second to last paragraph:
"Initially the two youngest children were going to sit on their parents' laps, but when their teenage son opted to travel on another flight - having had a seat booked - they seated Grayson in his seat instead."
That certainly sounds to me like the teenage son was rebooked on another flight. If that's the case, that seat didn't belong to (wasn't rented by?, whatever) the family anymore.
This is just getting stupid now.