"They specifically state that taxpayers who die before receiving the economic recovery payments are not eligible and are not allowed to keep them."

When the funds arrived in 2020 is not part of anything, now that you are working on the 2020 tax return. Here's why anyone who lived to see Jan 1, 2020 or longer, is entitled, as long as the tax return qualifies, too. Perhaps it would help to review what is really happening:

The funds were paid out as Advanced payment against a projection. The projection used 2018 or 2019 tax returns. But 2020 is the Actuals. You use the 2020 return to reconcile what a person is entitled to, against what they got.

https://www.irs.gov/newsroom/economic-impact-payment-information-center-topic-a-eip-eligibility

https://www.irs.gov/coronavirus/second-eip-faqs#Eligibility

One for each EIP.