in my 11th year after diagnosis, when undermedicated, my voice becomes very soft, i stutter, and my balance worsens. when "on", i'm ok.
i'd talk to his dr. on increasing his sinemet if he's on it, you mentioned he was on it in previous posts, assuming it isn't too high already, and if that helps, maybe replace a little with mucana. but imho the most important thing is to increase his quality of life, if he can't exercise and is depressed that will like have a worse affect than increasing his meds. but you need to talk to his doctor armed with the best info you can find. exercise is very important imho.