I can understand your concern about your father's health. Shaking is a very common symptom, especially in older people. 62 is not very old!! Have you talked to your father about your concern? In Parkinson's disease the shaking (which, by the way is not always present, at least 25% of patients do not shake) starts on one side of the body and is typically present at rest, To illustrate this and compare Parkinson's with a very common shaking condition (called Essential Tremor): when a Parkinson patient pours himself a drink , he does not spill any,,even, though moments before he was shaking badly. The ET patient will have difficulty trying to stop his shaking hand and often spills his drinks.
I do not consider a chiropractor to be sufficiently medically qualified to diagnose accurately what is wrong with your father. Your friend is correct , there is no cure for Parkinson's disease. This outlook is very difficult to accept , so a lot of patients seek alternative treatments . Beware of exaggerated claims of success.
Best wishes and talk to your father first.