Knee pain - No swelling - Non obese man.

My father is experiencing knee pain since years. The exact location of the pain is front knee cap. There is no swelling on either of the knee joint. Initially the pain was in the right knee now since 1-2 years it has shifted to the left knee. Especially in winters this pain gets worse. I have a doubt that he may be suffering with Arthritis as he feels pain in some other joints also but I am not sure because there is no swelling in any of the joint. This pain becomes an every year tale now. It comes, stays for 1-2 months then gone. But this year it's bit severe and now started moving towards the foot. My father is an healthy man. Non diabetic, Non obese man. Many a times I asked him to consult a doctor but he always resist to do home remedies. Please guide me what could be the problem. Is it fixable by home remedies / exercises or there is an immediate need to consult a doctor. Thanks, Piyush Bharadwaj