Before departure the captain had allotted the "leg" to the second officer (?) who was in the RH seat. Seemingly by default, the captain on leaving the cockpit for crew rest, handed over control to the junior pilot simply because it was his "leg." The real first officer who now replaced the captain in the LH seat, was clearly subordinate to the second officer purely because it was the second officer's "leg"
Surely, common sense should have dictated that before the captain left the other two up front on their own - especially since the weather radar showed storms brewing ahead- he should have nominated the first officer as temporarily in charge as PF since he occupied the captain's seat. As it turned out, the real first officer who occupied the captain's seat as PM sat on his arse and did nothing for fear of taking over control on the other guy's "leg" All he apparently did was to watch the second officer completely lose the plot even though it was obvious that the second officer was quickly out of his depth.
The seemingly sacrosanct policy of a captain giving a co-pilot a "leg" then being reluctant of taking back the co-pilot's "leg" for fear of causing offence, is idiotic and may have been a contributing factor in the utter confusion that followed.