A number of characters disappeared during the journey, either died or left the family. It looks like the novelist John Steinback removed them on purpose.

I think part of this might have had to do with the animal-like existence that these families had to endure. They lived a Darwinian type of life where only the fittest survived. The old and the wak died leaving only the strong and lucky to survive. This is the shame that America reduced these families to.