On the return trip the plane was not suitable for the IMC condition. This is critical. Was the P1 aware of this? Did he check his instruments on departure (of flight one and/or two). Was this perhaps discussed with/by the passengers who were to fly the twin?
W&B did not play a part on the return fatal trip. It is only there to show how curious it was that the first flight took place at all.
Currency of P1 made the flight(s) illegal but not necessarily lethal.
So the return trip which was the fatal one is the flight to look at.
I too am curious as to what outside factors were so forceful that they should override the P1's responsibilities and more important the P1's authority which prevented him from taking a no-go decision.