My response in blue:
1. We are retired...will that have any effect on his being able to be rated 100% disabled?
No, that's irrelevant.
2. Will this new diagnosis of Parkinson's make a difference in his current rating to be able to change his current rating to 100% disabled?
Most likely it will make a huge (positive) difference.
3. Since he is already being treated for this at the Veterans, might they automatically change his rating or does he need to re-file for a new rating?
Nothing is automatic. He will have to apply for the upgraded rating.
The thing to do is get expert (free) help from a veteran's service organization.
I'm a DAV member (Disabled American Veterans) and they have a magnificent network of service officers who will be happy to help document and file VA claims. Look here for starters:
https://www.dav.org/veterans/find-your-local-office/