The IRS just wants to verify that all RMD's were taken. You can enter that he took the full amount while he was living. Taking less than the full RMD would trigger penalties, which is not right in this case.
Select yes to full RMD and enter all of the distribution was RMD. This just allows the program to move on without trying to tax the money. It doesn't affect your actual tax form.
I am so very sorry for your loss.

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