The classification of these kinds of operations is a pustulent regulatory sore that's been running for decades. It's one of the many inconvenient and embarrassing aspects of the NGA ditching. But I do note that it seems to me that, on any analysis, the flight nurse and doctor were crew, not passengers, and that complicates things. A lot ...
But don't worry: It will all become crystal clear with the new, simple, outcomes-based classification of operations rules in 1998.
(On the proper defendant question, I would have thought the employer, the AOC holder, the PIC and CASA would, at least, have all been named or joined as defendants.)