What is the authors most likely purpos for writing life isnt fair

He believes fair only exists as a rationalization or justification. There is not such a thing as "fair" or "unfair", different situations are chances,  you can choose to overcome the odds and to leave the world better than you found it.

the penalty for defying creon's decree is death, as can be seen in the tragedy. if you do obey him however, all is forgiven

rudy is the nazi ideal, unfortunately for the nazis his ideal comes in the form of jesse the complete opposite of those who embrace the idea of white supremacy. over the course of the novel, rudy learns that he wants nothing to do with the hitler youth, and because of this his parents are forced to make a bargain; rudy's father is forced into the military, so that his son can remain home.   both liesel and hans influence that young man that rudy becomes. following han's example, rudy puts aside his own hunger to risk his life so that the jewish prisoners might have bread to eat.