POA not valid, but seller wants to get rid of house for mother

[Gunnar Sevart]

Working with a seller in DC that is acting on behalf of his mother who has dementia and is in the hospital. Without realizing that his POA was not valid (until our trusted title company informed us of the incorrect documentation) we now have a contract with someone who cannot legally sell us the property. The seller wants to help his mother get rid of the house, but I am unsure of how to proceed if the mother cannot legally sign off on anything. Thoughts?