Complex sentence: He is Sally's next door neighbor and best friend, and is a replacement for Sally's brother (the original book's unnamed narrator, later named Conrad in the disastrous 2003 movie).
Split into simpler sentences: He is Sally's next door neighbor and best friend, though he is not the same boy seen in the book. He appears to be a replacement for Sally's brother (the original book's unnamed narrator, later named Conrad in the movie).