I too had a diagnosis of familial narcolepsy many years before diagnosis of PD. There is a strong correlation between sleep disorder and PD. In fact, a current research supposition is that the sleep-disorder maybe be related to or even cause alpha-synuclean misfolding and build up of Lewy bodies that leads to Cell death and progression of PD. Sorry, that was a mouthful.
The problem for you and your family is that so very little is understood about PD let alone PD and its co-mornodities, so much for researchers to learn. Rx titration is guesswork for all concerned. Co-morbidities still seem to confuse more than reveal.
As someone who has had a PD diagnosis for 15 years, I feel I can make one strong recommendation: find a PD facility that uses an intergrative approach to Care. What I mean by that is that your father will do best if he has several specialists of different aspects of his PD who talk to him, his family and, most importantly, to each other. PD is such an individual experience. It will take a team to tease out the details of your father’s own unique version the the disease and how best to help him.