Not being a doctor, I can not say one way or the other if it is Parkinson's disease. Tremors can be caused by many things. However, here is a link to the Parkinson Desase Foundation describing Parkinson symptoms http://www.pdf.org/en/symptoms . It would be my suggestion that your husband makes an appointment to see a Movement Disorder Specialist. They can be found at most university hospitals, and the bigger hospitals around the country.
For your husbands sake I hope it is not Parkinson's. If it is, know that the diagnosis is not a death sentence. With proper medication he can continue to lead a good life for a long time.

GregD