What if... and this just occurred to me, but say Wo Fat's father was in charge, and Wo Jr. was an underling (or in the military or whatever you say), but it was WF's *father* who ordered the car bomb that killed Steve's mom... and then Joe killed Wo Sr. because of that (or Steve's dad did and Joe lied to Steve when he said that he did it).

But... if I stick by my original theory that Shelburne is Steve's mom and she didn't die in the car bomb, then that explains why Joe is helping Hiro... because Hiro/Koji would have helped to fake Steve's mom's death... for whatever reason.