Imminent sibling estrangement due to lack of concern and money. How could someone dishonor their parent and live with themselves?

I apologize in advance for my rant, but I just have to get this out. My mother passed a few months back. For the most part, she had her legal affairs in order with her 3 children as equal beneficiaries per her will. The only exception was an insurance policy left to an older child many many years ago with the expectation that the older sibling would look out for the other 2 younger siblings. I truly believe it was a complete oversight as to why my mother didn't update the beneficiary information.

Fast forward to today, all sibs are fully grown and that older sibling didn't lift a finger during mother's four year cancer journey. They may have visited a total of 5x for a total of 10 hours and maybe called once a week if that. Reason given "I'm busy".

I know there is nothing I can do if this sibling decides to keep that entire insurance policy. I was the one who scraficed and cared for my mother and would do it again. My other sibling helped me out as much as they could and fully supports me. So my question would be how could someone dishonor their parent and live with themselves knowing full well the intent of their parent wishes? I have much faith and I shutter to think what's going to happen to this soon to be estranged sibling.

Thanks for listening.