Don't know whether anyone will pick up on it at the enquiry stage, but the manufacturer of the minibus involved does not recommend towing a trailer - the reasoning being that the trailer can interfere with an emergency exit (ie the rear doors) - leaving only one exit - the side door - for the passengers in the main saloon area.
Im sure that in the circumstances of this incident, this issue probably would have had no bearing on the survivability or otherwise, but its a point that may well be raised.