The Ball Brothers are joining a new family -- the Roc Nation Sports fam -- with LaMelo, Lonzo AND LiAngelo Ball all signing with Jay-Z's agency.
The move was made official on Monday ... with Melo's business partner Jermaine Jackson saying the whole family was on board with the move.
"This was a family decision," Jackson said in an interview with ESPN. "This is now an extended family. They put together a beautiful game plan with Jay-Z."
Jackson added ... "I've known Jay-Z since I played for the Knicks, but this is what the kids wanted to do.