Hello Iris11, you really need someone more knowledgeable than me - but I notice no-one has responded to your post, and i didn't want the day to end without a reply.
So I'd say: This sounds to me like symptoms caused by the drugs not the PD. And I don't believe there's any reason to think drug-induced symptoms don't get better once the drugs either settle down or are changed. How long has your brother been on the new regime? What are the new drugs? And - crucial question - do you have a PD nurse?
If your brother's been on the new regime for more than a couple of weeks, and it the symptoms are getting worse, I'd suggest he got back to the neuro, GP or PD nurse (start with the nurse) and ask what's going on. If you're still worried, ring the PUK helpline (no on every web page).
(How'm I doing Turnip??)
Hope things improve soon, I'm sure they can.