I'm not sure what year Civic your brother has, but I found some info on civinfo straight from Honda about this issue.
Quote from PDF file (since you have to sign up to view the PDF)
3rd gear difficult to select, jumps out of gear or crunching when changing up from 2nd gear on 2007 model Type R only
Fix: Please replace the third/fourth synchro hub using the following information on your warranty claim
Casual part number: 23623PNS316
Sympton code: 0301
FRT: 5.9 Hours
Replacement part number: 23623PNS326
Another solution besides replacing that synchro...
When I was researching these cars (considered buying one at one point), I read about third gear grinding issues. The solution a lot of the time is to switch to GM transmission fluid, as seen here on an EM2
Here's another instance
It seems like a pretty common solution to use GM synchromesh. I found a few threads where it cured their issue on various Hondas.
Hope this helps