So this is from early childhood and I don't remember a lot. Here goes a blurred image of the plot.
A man is travelling in a train with his two sons. The train meets an accident with a lot of people dying. The elder son (s0) goes missing and the younger son (s1) is very depressed about the whole situation. Eventually s0 is able to find s1 but he has a very different personality now. Later it is discovered that s0 's spirit has been exchanged with someone else from the train accident earlier.
Keyword - Aloha Language - English
This was about 10 years ago. I remember something that sounds like the keyword being used often in the book.