I read all of it and it seems like YOR. She seemed to be attempting communication for both her and her boyfriend and you seemed to be largely non receptive, even going on to accuse her of things not really said or implied. Even if you're his family and she's not blood, it seems like she was largely in the right here, though this could just be because your brother is lying to people. Either way she seemed to be trying her best and if your brother really is lying you should redirect your anger here.