At times, father is shown as a loving parent and husband. how is that possible given his role as a nazi officer giving orders to treat people inhumanely?

When you mean "Father", do you actually mean the Fürher (Hitler)? The thing that is important to understand here is: Hitler was considered, before we knew all he had done, a charismatic and well, loving. Thing is, his kindness was only towards the Jews (and others, like homosexuals, disabled etc.) and those who were against his regime. The people of Germany wouldn't have voted for him or supported him if there wasn't a propaganda about the great qualities he had. Also, in his head, and a lot of his fellow nazi followers, Jews were not people but a pest to exterminate. Another final thing to understand is: nothing is perfectly black or white. Hitler looked in fact quite civil when you meet him (apparently) and kind and patient as he was also a vegetarian and loved dogs, however he still had this poisonous and hurtful mentality that led millions in the embrace of death.