JJ is the oldest of three Watt brothers playing in the NFL.
For the first time, he'll face Derek, a fourth-year fullback for the Los Angeles Chargers.
"It's very surreal," Watt said. "Even just being in a meeting, seeing him on the scouting report and flipping on the film. It's just like any other week, you're watching film but then all of a sudden it's your brother on the film instead of just a fullback. So it's very cool. I'm not going to try and act like it's not exciting or anything.
Derek and TJ played against each other last season, with Derek's team on the winning end.
The Texans played the Steelers two years ago, but JJ was injured an not able to play.
JJ said he is looking forward to Sunday, specifically the change to see his nephew, Derek's son. He's encouraging the boy to wear a Texans jersey and root on his uncle.
JJ also offered a scouting report on Derek ahead of Sunday's game.
"It's fun to watch him play. I love to watch him play. He's a great special teams player. He throws his body around as a fullback. He's willing to take on middle linebackers, take on guys on the edge. He can catch.
"When he made the decision to move from defense to offense, he's very smart. He's cerebral. He likes to think. I think that's why it made a little more sense for him on offense."