What Causes Difficulty In Walking And Loss Of Balance In The Right Leg?

This is a query regarding my father who is 68 years old. He is a diabetic and also undergone bypass surgery in 2002. Off late, he is finding it difficult to walk. His right leg has lost balance and slowly he is finding the same with his right hand. While walking or when raising from bed, his body is (more particularly his right leg and right hand) are shivering. Additionaly he is experiencing giddiness. Doctors told that he is having Diabetic neuropathy and last one and a half year he is using medicines for the same as advised by a neurologist. However we noticed that the last one year his condition has deteriorated even more and slowly getting bed ridden. Recently one week back we had his brain scanned which doctors told, has no issues.