Frankly, there is very little that a person can do to get another person to stop using substances--- pot or anything else. You can let your brother know you are there for him, and you can help him find treatment-- IF he decides that he wants it. You can decide to avoid being near him when he is high. You can live a good, clean life, so that maybe some day he will want the happiness that you have. But you can only change your OWN actions-- not the actions of someone else.
Sometimes the pot can stop people being agressive. maybe thats why he smokes it, i know the gov claim pot is bad. but its actually a relaxent.
he maybe taking something else if his agressive, or something thats stressing him out or on his mind, pots probley just helping him out.
sit down n talk to him. pot will not make him harm his wife or kids.. pots not that dangerous.. :l