J.J. Watt's Bro: 'I'm Extremely Proud of Him,' We're Not Done Yet!

J.J. Watt's younger bro, Derek Watt, isn't just praising his brother for raising $27 MILLION for Hurricane Harvey victims ... he's getting involved, too!

Derek -- a 2nd year fullback for the Chargers -- was loading up trucks at the "Chargers Food & Supply Drive to Aid Hurricane Harvey Relief Efforts" in L.A. on Wednesday ... along with several teammates.

Watt says he's been texting with his family about J.J.'s fundraising -- and thinking of other ways they can help out.

You gotta watch the video ... Derek says he's "extremely proud" and vows to help push the magic number to over $30 MILLION.