Sorry for your loss.
If the house was actually owned by the estate and the 1099-S is in the estate's name, the executor needs to file an estate form 1041 tax return. The executor/personal representative must file a 1041 if the estate has gross (not net) income of $600 or more. See page 4 "Who Must File" https://www.irs.gov/pub/irs-pdf/i1041.pdf
The cost basis would be fair market value as of the owner's death, probably resulting in no gain or a loss.
I say if the home was actually owned by the estate because that can be a tricky question. In some states the home is immediately owned by the beneficiary after the death of the owner, subject to pulling back into the estate to pay debts. Other states that is not so and the estate owns the property until the executor sells it. That is a question for an estate/probate/trusts attorney in the state the house was in.
While you can buy Turbotax Business (not home and business) to file a 1041, this is pretty complicated and you may be best seeing the advice of a estate/probate/trusts/tax attorney or a CPA or EA who works in this area.
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