I'm sorry for your loss.
In fact, your dad is eligible for both stimulus payments. If he did not get the second stimulus, you can claim it as the Recovery Rebate credit.
Only individuals who died prior to January 1, 2020 are not eligible for the Recovery Rebate Credit.
Please read question B1 in this IRS FAQ.
**Mark the post that answers your question by clicking on "Mark as Best Answer"
Actually it's question B12 (unless you made a typo).
Or.....For deceased individuals see the second question under Eligibility. If they died in 2020 they still get it.