I can't believe how much you're going through, and all at once! But honestly, you really sound like you're holding it together amazingly well - with grace, humor, wisdom, etc.
I definitely agree that your brother should not be allowed at the wedding. That sounds like a nightmare.
If you can, do stay anywhere but under the same roof. There has to be consequences for his behavior, and so far it sounds like he's been living consequence-free. Your being alienated from him is a consequence he will have to live with.
Good luck and congratulations on your wedding. I am so sorry you're going through this. I know you dont' want to alienate your parents, but verbal and physical abuse is a very valid reason to cut someone out of your life, at least temporarily.
It sounds like he is jealous and immature... you are so above that its redicuous. I would ignore his existance and remove yourself from any room that he is in for the next week. Causing you to be upset and cry/ruin your special dress is what he wants, its what a 5 yr old would want too.
I would also UNinvite him from the wedding. Someone needs to cut him off.