I just learned that my father hasn't filed taxes in years. He is in a nursing home and has dementia.

His power of attorney is his girlfriend who has no idea what or when he might have filed. He hasn't had a job in years and has been disabled for a long time. I'm not sure if he would have had to file but he did own a home with a mortgage. Somehow he made mortgage payments until 2 years ago. He now can't answer any questions and no one seems to know where any paper work is. His girlfriend has sold the house and after the mortgage is paid off, the proceeds will cover past due property taxes. There is nothing else left - no money, no insurance policies, no property. Should we try to make his POA file past due tax returns? There is nothing left to pay any taxes - again, not sure he would have even had to file as we think all he got was SS benefits. Who could be held responsible? Thoughts?