this is a story that is common in many subs on. does your parent see him as a golden child. they often neglect the other child, and when things get bad, usually financially for the parents because they gave all thier money to said golden child and he mismanages the funds.
him killing animals is a sure sign of sociapathic/psychopathic tendacies, its only matter of time before you or your parents will be the next target(s).
it seems like the parents want to keep you in the house to truncate some of the brothers anger and violence towards you instead of them.
are you going to college? if so there are scholarships that can assist with living in dorm, or a off campus apartment. at least my state school has an offcampus apartments that they own, usually only for universities/state uni.
eventually the parents are going to rely on yuo financially or otherwise to offset thier retirement, if your bro doesnt harm them first. this only ends poorly.