You should really brush up on your history. It’s estimated that up to 77,000 Germans who were a part of the resistance were executed and an additional 800,000 were arrested. You’re right that Nazis didn’t kill other Nazis, they killed Germans who resisted Nazism.
https://archive.org/details/encyclopediaofge0000unse_i6r5/page/n5/mode/2up
My setting has a lot of nautical aspects to it, including lots of drowned and sea creatures. One of my players in a captain of a ship (they’re all level 15+ now, so he’s worked his way up there). I’d have the blind character have a parrot that narrates the world to them, much like a DM.