I am very sorry for your loss.
Regarding the 2400 you returned, 1200 of that was allocated to you. Since you returned it, you will most likely need to claim your half as a credit on your 2020 return. The stimulus payments are actually an advance on a credit on the 2020 return.
Turbo Tax software asks for a death of someone, but not ask for this information for stimulus credit. It would seem that this question would be asked on receiving stimulus. The IRS already ruled a deceased person is not entitled the credit. Why not include in software the process to prevent getting the credit for a deceased person?
When you are finished entering your tax information in TurboTax for 2020, you will go through a review process at which time you will be asked to enter the amount of stimulus payments you have received. You should enter the net amount you received for the first and second round of stimulus, after you factor out the money you returned. This should result in the balance due you being applied to this year's tax return.