What is the Process of Getting a Diagnosis?

My husband has exhibited signs of something for 10 years. He is a once confident man now unable to make decisions, cannot handle any stress, and displays a total lack of confidence to do things he never would have thought twice about. He has REM sleep disorder (since 2015). He has stiffness. He walks like an old man--he is 59. He has trouble finding words. His speech has become quiet. He retired from work two years ago because he simply couldn't handle the stress, and now works a few days a week at a golf course (which he loves). His father was 62 when he died from complications of Pick's disease, which was horrible to witness and greatly affected my husband. He has been in denial for years and has left me to "stew" with what I witness (causing me major frustration and anger). I tend to face things head on, but this is not happening to me, so there hasn't been much I can do other than be frustrated that we could be doing SOMETHING to slow down progression. But now, he has finally admitted to his GP that he has all the symptoms of Parkinson's, which in a way has lifted a burden from me (although I can't even imagine what we are facing, but we will face it together). We have an appointment with a certified nurse practitioner who specializes in Parkinson's and movement disorders. Does this type of practitioner actually diagnose or are there other tests that are completed before a diagnosis? Please share what the process is for getting a diagnosis and what we can expect. I'd like to be as prepared as possible and of course, we are worried. I will need to be his rock. Thank you in advance.