Can my father take additional loan

I am looking for a legal advice. My mother has invested on a property in my home town, paying from her paycheck from past 20 years and house rents. Being an Alzheimer’s patient she lost memory and can’t talk. My Dad lived with another woman throughout his life. He used to collect rents and pay house loans, after my mom fell sick. Now He got loan closing certificate and trying to get house original documents. Can He sell or take additional loan amount using that document. The property is in my Mom’s name , cleverly he has doctors certificate claiming my MOM cannot talk or read . He don't have kids of his own from another lady Thank you