In But, Not Buddy by Christopher Paul Curtis, what is the difference between Deza's family and Bud's family?

This is a fairly straightforward question and answer.  The key difference between Deza Malone's family and Bud Caldwell's family is that Deza's parents are both still alive.  
In addition to Deza having living parents, she still lives with her parents, too.  They might all be in a shantytown together, but at least the family is still in tact.  Contrast that with Bud's family.  Bud has never known his father.  The main plot of the book is Bud attempting to find his father.  He never does, but he does find his grandfather.  Bud's mother is no longer alive.  She died several years before the book begins.  Bud doesn't know why she died, but he does tell readers that she was sick for about six days before dying.

I said, "I was six years old when it happened, sir. "I don't know why, she was too sick to go to work for six days in a row, then one morning I went into her room and she was dead. But she didn't suffer or nothing, it happened real quick, she didn't even have time to close her eyes, she didn't look like it hurt or nothing."

Bud has been living in orphanages and foster homes ever since his mother died.