Do you think German citizens, such as Alex steiner and Hans hubermann, were justified in showing passive acceptance to the Nazi regime? What else might they have done?

I would say they were justified. They really had little choice but to conform or secretly resist the party. If they were vocal, they most certainly would have been severely punished or killed; the whole family would be in danger. It was far more effective to passively resist the Nazis. Acts like secretly helping Max, did much more against the Nazis than simply being vocal and being killed.

Why do you think the Hubermanns insisted that Liesel call them "Mama" and "Papa"?