UP: I think my little brother is lessening on the undying hatred of me. (Every day so far has been "is she going home yet? has she left? when does she leave?") My mom explained how I have another family to visit, too, and once he got over the incredulity that I wouldn't be completely satisfied with this family (don't think the "you don't get a choice" thing has sunk in yet, though I may be helping with that!), he decided I "wasn't too bad". Perhaps that will help lessen the perception that I'm a threat to his family unit.
IA: Part of the change in behaviour included screaming, hitting, peeing, and biting (thankfully none of it at me). Major, major meltdown with my mom before she laid down the law and he decided to behave better.
Definitely leaning more and more towards being the cool aunt/big sister, and not having kids of my own. These boys are cool, but I am VERY glad I'm only here for two weeks.