My Dad has had Parkinson’s for 17 years, and while his balance is now severely affected, getting him to continue exercising in some shape or form is key really to try and reduce his balance issues.
He has been seeing a physiotherapist once to twice a week for the past 10 years, and that has really helped. He is really tired after each session but the physio is pushing him for good reason. My mum accompanies him to some of the sessions, and the physio explained to her how to help Dad get back up if he falls, without injuring herself (back pain etc.).
Re: food - he has some issues with swallowing etc. which happen more and more now that the illness is progressing. A registered dietician could also put you in the right direction re: meals and food. He sometimes have muscle pains in his legs at night, and tries to eat a banana (potassium) evening time before going to bed to try and release the cramps etc.
Also, we found that the use of a special chair with arm rest at the dinner table helped prevent falls etc. and was much better than a normal chair, especially with his low blood pressure (he’d easily faint after meals etc.).
Hope that helps.