Amending an amended 2023 return for deceased and incapacitated parents

Last April my elderly father used the desktop edition of TT 2023 to file returns for himself and his wife. A month later, he used TT to amend his returns on the advice of Intuit. (There was a bug in TT's handling of Oregon state returns.) Unfortunately, he made some errors with significant tax consequences, e.g., failing to include Schedule D. He has since passed away, and I'm trying to amend his amended return for 2023 so that I can move on to their return for 2024. 

I updated the 2023 return in TT (which seems fine with amending an amended return), and I think I'm ready to file it, but I have some concerns:

• Since my father is deceased, he can't sign the return. My mother can't, either, because she has significant dementia. How should the return be signed?
• The amended return yields a refund, because the Schedule D I added shows a loss. The house my parents lived in when the returns were originally filed has been sold. How can I get a refund check sent to a new address?

Thanks for your help.