I can't claim to know much about Parkinson's disease but have known some people with it. In case you haven't found your way to good information on the Internet, here's the Mayo Clinic's material on it:
https://www.mayoclinic.org/diseases-...s/syc-20376055
You'll notice that it states that there is no test that can be given to diagnose it.
Sometimes the medicines that are given for it can have fairly serious side effects, but sometimes they work well. One person I knew was on carbidopa-levodopa but had to stop it fairly soon after starting it.
That isn't very encouraging news, I know, but unfortunately Parkinson's disease can be a bummer. I'm so sorry your father has this diagnosis but hope you can find the information you need and can help him.