can playing basketball promote teenagers growth?

I believe your brother is right. Playing basketball helps you lose weight and the lighter you are during your brothers age at the time the more likly you are to be taller because gravity does not have you down as much. Cardio such as basketball or any other cardio also boost HGH(human growth hormone)levels. I played basketball the most during my middle schools years and I also grew my tallest. I basicly played it almost everyday and was skinny.

When your brother was playing, it was in his main growth time. He would have grown whether he was playing basketball or not. However, playing any sport can assist in growth as it promotes good health, builds muscle tone, strength, etc, all of which would help in growth.