"CORRECTION to post. if it matters, line 3 was answered no, not yes"

Are you dealing with someone having SSN that is not marked as valid for work? Or, doesn't have a SSN?

There is no one that would be subject to a Split between EIP 1 and EIP2. There is nothing variable about 2020; it's either Yes or No, they qualify. Not by month of death.

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.

It might help you to refresh the qualifications for stimulus/impact credits/Payments:

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.