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Please ignore the discussion topic, I had to pick something. I remember reading a book in eighth grade that I loved a lot.
This kid and his autistic older brother live with their very neglectful aunt and uncle, and the kid tries really hard to take care of his brother. I remember the brother's special interest being cars or mechanics. So, this kid somehow ends up in a party at this huge family's house, and they go to the beach. The kid really likes this family, and somehow ends up staying in their house by hiding in their dead mom or dad's study, where nobody goes. The family just thinks he hangs around their place a lot. Eventually, one of the sisters discovers him and helps him hide for reasons I also can't remember. I also remember her accidentally covering him in glitter somehow, if that helps. They end up getting together. Eventually it comes crashing down at a sort of beach party of some kind? I just remember the girl making the kid some kind of tailcoat for it. That's about as much as I can remember, the endings really hazy for me.
Hope someone can help out!