My advice is to call Adult Protective Services. They can visit the son at the hospital and determine whether or not he wants to speak to his father or is even able to do so. If he does not want to speak to his father, then it's perfectly legal for the son, or the son's agent (the mother) to instruct hospital staff to not put through any telephone calls from the father.
As far as answering medical questions goes, since the son is an adult, only he, or an agent under an Advance Health Care Directive or a court appointed Conservator, may be provided with confidential medical information. If the hospital were to disclose confidential medical information without the permission of the son, or the health care agent, that would be a violation of the Health Insurance Portability and Accountability Act (HIPAA) for which the hospital could be subject to a fine.
