Sadly the answer is in your question. If your dog realises that he is safe with your brother it will be easy to change the dogs behaviour with training. Your brother is the issue here, not the dog. How you can change your brothers behaviour, I am not sure, but I would sit him down and tell him he is being cruel to the dog, and that the dog did not choose to get picked on. He needs to respect both you and the dog. I am sorry for your dog.

Let him get bitten, then sit him down and explain to him why this happened. As Tani said, it is not the dog's fault.

This is entirely on the fault of the humans in the house. Your brother specifically, but all of the humans. How old is your brother? Why are your parents not bestirring themselves to put a stop to this inappropriate behavior? Not to put too fine an edge on it...people who enjoy harassing and tormenting animals generally end up harassing and tormenting HUMANS at some point in time. Case in point most sociopaths started out life causing harm, physical or emotional to ANIMALS. Pretty much all the best kooks did it. If your Parents are content to ALLOW this behavior, you have an even larger family problem brewing than your dog represents. I don't know how old you are, but I would lay it on the line. Talk to your parents, tell them what has been going on and your fears. I would also tell them that if they do not support you in protecting an innocent animal YOU will not be responsible for the outcome. If things don't change for the better, make some phone calls. ASPCA, CHILD PROTECTIVE SERVICES...speak to them about it, without giving your name or address to start, call it a fact finding mission. Does your brother also pick on you inappropriately? I'll admit, while I normally am a very relaxed, nonviolent person...NO ONE has ever gotten away with abusing an animal in front of me...or a child, these are the two things that open the door to me going bonkers and the abusive person begging to be let go of. I'm NOT suggesting that you physically take on your brother, but do what you must...using intelligence, to protect your dog.

Your dog apparently does not like your brother...and from what you say, he has good reason. Anyone who torments an animal deserves to get bitten. It is bullying and chances are he will treat people who are weaker than him the same way..if he is not already. Your brother is the one whose behavior needs altering..the dog is simply trying to defend himself. The growling and snapping is a warning to leave him alone.