curiosity killed the cat...satisfaction brought him back
in your last scenario, going below DH without visual cues, all the non flying pilot has to say is:
if you go one foot lower I'll report you and I will move up one seniority number.
by the way, at DH if the pilot(s) see the sequenced flashers only, they are allowed to continue to touchdown zone elevation plus 100'.
The instrument approach at virtually every decent airline is well orchestrated, choreographed and things rarely go wrong
But if the captain went below minimums and was not responding to the first officer, the first officer must ascertain if the captain is incapacitated, and if so, take control.
we call it the 2 communication rule...captain, you are too low, captain you are too low, I am taking the plane
this happens pretty darn fast
you have interesting questions, besides curiosity, what is YOUR REAL reason for asking