What should I do to help my wife and his son who has bipolar disease?

I live in Florida. I am originally from Africa and I'm married to a USA citizen. I was married since 2010 and they just granted my immigrant visa this year, in month of June and I came into the country in August. I thought it was going to be easy to live with my wife for the rest of my life but there is life threatening. The first born of my wife who is going to be 16 years old this month was diagnosed bipolar and very aggressive at times. I have been abused by this boy several times and which I wrote and recorded most of the scenes of events. He even smacked me in my private part when I was asleep and I cried until the second day. He showed me bullets after he went into his mom's drawer and ask to me if i know that I could get killed if he placed a kind of pulley behind the bullets. He even locked himself inside the trunk when I was about to go pick his mom from work but I saw him before he locked the door. He jumped at the back of the truck. Again when I was about to go to a busy road and I had to stop at the middle of the road and tap his butts. He reported the case to the father and he lied that I hit him without any sign nor mark or scar of injury or bruise(s). His father threatened me and he started pointed finger on my face and shouting while the kids were there. I love my wife and my wife thought knew this boy is not of well behavior and name calling is part of his chauvinistic behaviors. I love my wife and she doesn't want to lose the kids. He says to me that how he wish his mother (my wife) were dead of die at the moment he was talking to me this morning. This is not my first time of hearing him saying this and he said this to his mother. I found a sheet of paper on the table this morning and i saw a message from his a "brotherhood" asking him some nasty things to do if he would like to join them. Most of the words there are concerning killing hundreds of people and even deny or betray his country and ready to commit suicide.