בס''ד
The Rambam (Maimonides) teaches us that תחיית המתים (techiyat hametim - the resurrection of the dead) will be a miracle that HaShem will perform, and therefore it doesn't matter if the body has been buried for thousands of years and has almost completely decomposed or if the German Nazis יש''ו שר''י burned the body completely in the ovens of the death camps. Those who merit being resurrected will be resurrected miraculously regardless of the state of their body.
But sadly I must add that those who knowingly defy G-d's mitzvot (commandments) risk not being part of the resurrection. There are preconditions to earning the right to eternal life, and one of them is obeying G-d's mitzvot. I am not judging anyone and I don't know what G-d will do with Jews who knowingly desecrate and deface their bodies with the pagan ritual of tatooing or who cremate their bodies. But I do know that it is absolutely forbidden to engage in these practices, and that at the very least a Jew who does so is risking losing everything on the day of judgement. Of course, if someone does so out of ignorance, it is not the same as someone who knows better and has been warned.
In Judaism, the body is SACRED. G-d created the body as our tool to fulfill His will in this world. And we must do so the way He commands us to. G-d didn't give us the 10 suggestions or the 10 options, He gave us the 10 COMMANDMENTS. And to the Jew, G-d gave 613 commandments.
fidei, by saying that you will do to your body what Hitler did to the bodies of defenseless Jews is something I cannot comprehend. Are you allowing the Nazi mass murderers to make the rules for you? Hitler sets the standard for what you do to your body? If you really want to defy and defeat Hitler, and if you really want to honor your loved ones, then I think you should do what the Nazis would not want you to do - you should be stubbornly loyal to your Jewish faith and heritage and commandments and show the Nazis that they did not defeat you or break you, and that the sacred Jewish faith which the Nazis detested will gloriously live forever, while the Nazis and all other Jew-hating Amalekites will burn forever in the deepest bowels of hell.
As for your father, he did not realize what he was doing, and so we must pray for his soul. Your father was among תינוקות של בית רבן (the innocents who sin because they did have a full Jewish education). I am sure that your father was a good man, and we love him and we will pray for him. But you can do something now for his soul by correcting this mistaken path and doing what Judaism teaches us to do. And by convincing your mother הי''ו (HaShem should protect her and give her life) to also do what Judaism commands.