I think that your questions are very good in how they force students to re-consider the simplicity of typical narratives. The roles of the perpetrators can be difficult to understand, not only because the Holocaust is such a mammoth act that was put into place in a systematic and complex manner, but also because some of the guards in the novel are more humane then others. This is an important concept for students to learn because, when studying the Holocaust, it is crucial that students recognize the complexity of how it was put into place. This makes them see the Holocaust as carried out by many humans – human who, in many cases, were not barbaric but found excuses for what was happening. The problem with a lot of Holocaust education is that it turns the event into a “museum piece” that is so far removed from experience that it seems like an alien thing that just happened. Having students learn about the complexity of it makes it easier for them to see how it happened.
I also think the denial, and having Eli be mad at his father, are important details because it also goes leaps in showing how human behavior was always at work in the Holocaust. Humans are flawed and act in irrational ways sometimes, and even though this makes for messier and less-clear “narratives”, it is essential in making human students connect to literature and to history. Historical empathy only can occur when students see historical figures as people who lived instead of characters in a narrative, and I think that the answer to your questions are more about recognizing why he included those details in the book instead of the psychology as to why they did it.