My question also... and his not supposed to know what his brother did to Jaewon... or am I wrong?
he at least knows his own brother got involved
This was super confusing to me, too, and after using Google Translate, I think it was an incorrect translation. Granted, we know that Google Translate isn't always the most reliable so I could definitely be wrong, but I think it was supposed to say something like, "I heard all about what happen from my brother." If that translation is correct, that would make much more sense since JW did hear from his brother about everything that the brother did to Jaewon.
he said 'I knew what HIS brother did to him' -- was that not JungWook speaking or did they mean 'my' brother? Or did I miss something lol