mrbigbird, if the hijacker(s) gained access to the cockpit, the number of passengers in the cabin is totally irrelevant, so even a lone hijacker could carry out the takeover (although two to four would be more likely).
The doors between cockpit and cabin fitted to all wide body (and most narrow body) airliners after 2001 make it impossible for the pax to gain access to the cockpit - and, given the hour of the day that these events took place, it's quite possible that no one in the cabin, perhaps not even the First Class cabin crew, would even be aware that anything was amiss for quite some time - until just before the aircraft landed or ditched.