Why is the brother so evil towards his siblings?
Well, he's not evil per se - I think he might be some kind of sociopath, because of his lack of understanding emotions. I recommend reading novel with him, because I don't want to spoil anything :]
he is not evil but he doesn't understand emotions! he genuinely thinks he is helping chase like this but nope
he isn't, more like he doesn't understand nor process emotions. In his story, he found a boy locked up in the basement and tried to help him (helping him out by staying with him to 'finish his punishment rightly'?) and he did that purely thinking it would make chase take care of himself, to scare him into doing it. His intentions are pure, he just doesnt know it makes them worse, not better
chase did not do anything with a dog. his idiot brother is making him believe he did. chase dosent remember but it was Josh who he spent his rut with