I cannot see how your grandfather can respect a man whose selfishness caused the deaths of something like 50 million people, and sent children out to fight in a war that was already lost, many without even being given a gun being expected to find a gun of a dead soldier and the ammunition before fighting a strong well armed army of invaders. I assume your grandfather was not brought up in the main cities and came from a rural area where the people did not see what the Nazis were really doing and were getting their information that was given out by the German propaganda showing they were really nice guys. Hitler and his Nazi thugs believed people were only important if they helped the Nazis gain and hold power and believed people's lives beside their own were disposable on Hitler's whim. Before Hitler committed suicide he realised the war for Germany was lost and he verbally abused the German people for not making his dream of world domination become a reality. After all the German people did sacrificing their lives for Hitler and the Nazis he believed they should all die for failing him.
Many people who supported Hitler before the war did not realise how Hitler was manipulating them to set Germany up for war. The Gestapo (the German secret police) were brutal on the German people and a knock on the door was likely a death sentence whether you were innocent or guilty. The Nazis believed only perfect German people who supported the Nazis had the right to live freely, and anyone not deemed as perfect in the Nazis eyes were seen as slaves or should be put to death.
I assume if your grandfather was alive at the time he was only a small child and was sheltered from the realities of the Nazis, and likely his parents were supporters of Hitler's so all he heard about was the way Hitler had rebuilt Germany from its pre-war poverty. Most Germans didn't realise Hitler was borrowing heavily from neighbouring countries to pay for all Germany's new found employment programs and military build up, and his plan was to invade and conquer the countries he had borrowed from and not pay the money back. Many did not realise that the Jews, gays, disabled, gypsies, and other un-desirables of German society under the Nazis were being systematically being murdered on an industrial scale. The Nazis made propaganda films showing these people living healthy lives in beautiful camps being well cared for by the Nazis so the German people would not realise what a murderous political party the Nazis were. The German people did not realise much of Germany's money for the war came from the sale of Jewish assets and money confiscated from Jewish bank accounts after they were murdered.
Your Grandfather came from a different era and was exposed to people as a child with a distorted outlook on what Hitler did for Germany not realising how they were being manipulated by the Nazis. Many Germans could not understand why the allies bombed their cities saying why do they do this to us, not realising this is what the German Luftwaffe had been doing in other countries and the people had no idea of their cruelty and death their military was causing through Europe.
Your grandfather is not a bad man but we quite often develop our beliefs as children from what we hear and see around us. Likely your grandfather did not see what was going on in the cities and he and his parents and neighbours only heard the propaganda believing it that the Nazis were decent people and believing the allies were the villains for invading Germany and that the German people were the good guys. They had little idea of the evil the Nazis were doing away from their rural towns and villages.
Did you know that during the time of Hitler's power that 70,000 Germans were killed by the Nazis for speaking out against the evil of the Nazis. They were killed for being anti Nazi. Even listening to a foreign radio broadcast was punishable by death by the Nazi as they did not want the German public to hear the truth.