Unfortunately, this is an issue that the IRS will be reconciling. That is why SSA basically pushed it off to the IRS by telling you to put it into savings and hold onto it. The IRS does have a plan, and are feverishly trying to keep up with any potential overpayments of stimulus checks - especially due to the closeness of second stimulus payment and beginning of 2020 tax season. However, with your even more unique situation - and I am so sorry for your loss, by the way - even though he passed in 2020 (I am assuming he did, by the way, by your wording but I could be wrong), they are calculating it based off of 2019 information. Just don't spend the money because chances are highly likely that they'll come looking for it! If this makes you feel more comfortable, you could always make an appointment with your local IRS office (if that is feasible) and discuss with an agent. But you have done nothing wrong. I wish you all the best!
