I would wonder about re-evaluating the Parkinson's meds your grandfather is taking. I'm not familiar with 'syndopa'. I'm familiar with sinemet ... or levadopa ... but not syndopa. Are you in the US?
I agree that it would be best if your grandfather could see a movement disorder specialist or MDS. An MDS is a neurologist who specializes in movement disorders such as Parkinsons.
Everyone responds differently to different meds. I would ask his doc/neurologist/MDS about Parkinson's medication options. You could also talk with a pharmacist. They know, or have the resources to research, Parkinson's meds.
Best of luck!
Life is a dance. Don't sit it out. ---- Jackson H. Brown