Your brother is on the edge of a precipice. He is probably being prescribed drugs from a group known as "dopamine agonists", and although these are good for alleviating PD symptoms, they also cause potentially disastrous Obsessive & Compulsive side effects in 25% of recipients.
I was one of the unlucky ones. I was completely ruined by such a drug, losing £2m in all as well as losing career, home, family and friends, as well as getting divorced. I also got violent and had several problems with the police.
This link takes you to a press article about me: http://www.telegraph.co.uk/health/healthnews/6446763/Parkinsons-drug-made-former-councillor-carry-out-45000-eBay-ticket-fraud.html
There are hundreds of posts on this forum about people whose lives and finances have been totally wrecked by dopamine agonists, take a browse around. I also posted a poem called "Ray's Story" (or somesuch) here a couple of days ago, dscribing my exploits.
There are scores of different obsessions these drugs can cause, and most affected patients suffer from several. The most frequent are gambling, over-spending, hypersexuality, affairs, crossdressing, porn and violence. Most become secretive, devious and aggressive, and deny everything, claiming there isn't a problem.
Your brother needs to be deprived of any access to cash whatsover - his own or others', or he WILL lose it ALL. And plenty more.
Get him to a specialist A.S.A.P. Not just any old consultant neurologist but one who spcialises in PD, and who is bang up-to-date on all the latest drug information and research.
And show these posts, press articles and other cases you uncover TO YOUR BROTHER. Also to parents, relatives, friends, nurses, GPs and consultants - they need to be warned. They probably won't believe it, but they need to.
Good luck, keep us posted.