ANSWER - Dreams very rarely mean what we think they do and the meaning of dreams is a psychological issue, not a magical one. You could argue that your subconscious knows something you don't and is trying to warn you, which is a type of magic but that's not really important.
I can't give you an extensive answer as i don't know you but in my experience, a dream like this usually points to our own distrust of those we're close to. Is there someone in your family or your close circle whom you should be able to trust but just don't? Chances are it's not your brother at all, yet he is the dream's personification of that person. It could also be that it is yourself you are having the issues with and your brother is holding the gun to that part of you that "he" feels is damaging you?
With dreams, it's always better to look internally, rather than externally, for the answers.
My advice would be to get yourself into a meditation routine and meditate on the issue. Tarot cards are a good way to do this and art therapy is another.