Hello and welcome to Psych Central.
I really dont think that a physical and mental health asessment would hurt at this time to find out if your father in law is having physical or mental health issues. There are many reasons your father in law may be having these issues. I would highly suggest if possible having your father in law move out of the house for a bit with relatives, until there is a diagnosis for your father in law. I dont feel that your father in law is safe living alone at this tim, and perhaps will need a live in care giver in the future for his safety and well being. I hope things get better and straightened out soon for all parties concerned. Take care and good day. Soidhonia