There are a large number of foreign-trained physicians who have done the Nurse Practitioner route. Some schools have programs specifically tailored for them, where they get the BSN/NP simultaneously. That might be the path of least resistance for your Dad. If his undergraduate degree is “acceptable” to various nursing programs, he can quickly do a number of nursing prerequisites and apply to an accelerated nursing program (~15 months). He can work as a nurse, while pursuing his NP degree.
Physicians Assistant programs are very competitive in most states and there is no guarantee he can get into one after completing his PA prerequisites.