Hi there! I am so very sorry to hear about your. Dad, they are generally such special people and when they hurt, we hurt!. In the 1st place I am no Dr. But if it is in the mouth area it could be tmj(temporal mandibular joint) which can be helped some, asll the dentist and see what he suggests as far as the shoulder, it could be frozen, which is painful, he could have pulled a muscle which is also painful or he could have arthritis which is too very painful, I know, I have that along with other medical problems. It sounds like it is time for your dad to get a good check up, which I know is very difficult to do if you are a man.
Good luck!
I do wish you and your.Dad the best!