Doesn't sound like the bank has many beneficiaries who die eariy in the year. How can they put a March distribution on a Schedule K-1 for someone who died in January? If anything, it would come under the 65-day rule and be reported on the 2020 return. Did they know by March 1 that he had died? They surely knew by September 10 that the quarterly payment would not be needed.

Your job is not to clean up their mess. I don't see a reason to report any of the K-1 income on either the 1040 or the 1041 -- or to claim the ES payment, although IRS is likely to send it anyway, and the estate can decide whether to pass it on to the rightful owners, or return it to the bank.