Can't remember the title or author if this book

[Jerremy]

Hello, I am having a really hard time trying to find this book that I began reading in grade 8. It was about a young boy and girl (brother and sister if I am remembering correctly) that take a boat to this place in order to find their mother or something like that. I remember it involving some underground black market and a railroad. Some other little details I remember are: It had a ship stuck in a tree that someone was living in, there was a part where someone used a kite to set fire in a far off place. I am not sure how accurate these details are since I last read this book (but did not finish) about 4 years ago. Is there anywhere I should look? Like a book finding search? Thanks.