Personally I would report what your brother has done. He's clearly unstable and dangerous. The dog also needs to see the vet. While you shouldn't use violence against your mother, it was wrong of your parents to ignore your brother's history and then proceed to ignore the consequences of it. It's ridiculous that they are so caught up protecting your dangerous brother that they don't take your heavily injured dog to the vet. They are insanely irresponsible. Damn this thread made me feel angry -.-