What to do about a violent dog?

My family owns a violent dog. We think he may have come from an abusive home. He's very aggressive and protective. If someone is in bed he won't let anyone else in with them, he sleeps in whose ever bed he can. He's very protective of a male who is the main owner and was the first one in the house hold to really make a connection with the dog, and you can't get close to the male, you can't walk past him or the dog will growl and nip. He's a small dog some kind of a terrior mix we're not sure exactly which kind. We also have bigger lab which he is also very aggressive to. We need help.