A couple of inconsistencies in your analysis:
First, you talk about the chance of substituting someone of greater skill for the shot part of the event. The very threat of that is why the raffle ticket winner must be the one to take the shot. Just because these guys are twins does not mean they have equal skills. I have no idea whether they do or not. The fact is that the mathematical equation counted on the ticket drawer doing the shooting. Otherwise, whatever kid won the ticket raffle could simply give his or her shot to the best shot in town with the idea that they’ll split the prize.
The insurance analysis was not based on that, therefore the odds - and therefore the very heart of the insurability of this event - are based on the ticket holder taking his or her own shot. Period.
Next you then use the comparison of throwing dice. Not the same thing at all as a full court basketball shot or hockey shot or short par 3 hole in one type contest, etc.
I gave the exception of substituting someone with higher skill.
My point was that was all that mattered odds wise regarding having someone else shoot the shot verses the random raffle ticket winner. You made it sound like because the individual odds of winning each stage of the event were so much better that somehow the insurance company miscalculated the odds under those conditions (two different people at the two stages) of paying out overall.
And my final point, if the skill of the two twin brothers were essentially identical then the odds of the insurance company having to payout were unchanged regardless of which brother took the final shot. Something that you implied was otherwise.