Joanna,
As Ed/Yekkimo said, your brother has to come to terms with his situation. He'll undoubtedly share his condition with you when he's ready. He's lucky to have a sis like you who is so concerned. In the meantime you can educate yourself and be ready to support him when he's ready to tell others.
My husband knew right away because he was with me when I was diagnosed in 2001. I chose not to tell my then-mid-teens sons or other family because I didn't want them to worry. There wasn't anything they could do anyway and my symptoms were easy to hide. (Maybe that's how your brother is feeling now???) I/we still haven't talked at length with my boys about my diagnosis because I don't want them to be concerned. My brothers and parents pretty much understand the significance, although I haven't really needed their support yet.
I told my co-workers about a year after I was diagnosed. I thought some of my co-workers had noticed my tremors. However, when I did tell folks at work, it turned out that no one had a clue. But ... telling them relieved stress I was feeling.
Hopefully your brother in seeing a good neurologist or preferably a movement disorder specialist (MDS). Most folks start out on a medication that falls in the category of a dopamine agonist - usually Mirapex or Requip. Sometimes it takes awhile to get the dosage right and to work through some of the side effects - nausea, etc. There probably will always be some side effects to any pd medication he takes - is how it is.
Support from others is so important. It is difficult, however, for a person who doesn't have Parkinson's to truly relate to the situation. I've found pd chat rooms and pd support groups to be very valuable. They can also be helpful for caregivers, family, friends, etc. The most important thing is for the person with Parkinson's to educate themselves about their alternatives. They are their own best advocate!
Hang in there. Your brother will share his situation with you when he's ready. In the meantime you can arm yourself with information and be there for him when the time is right for him.
lizzy4451