Interesting that he still has an estate. And thanks for explaining what it means

Estate is a common law concept. There’s no direct equivalent in German law.

In practice, there was not a Hitler estate - the government of Bavaria (a state in Germany) took ownership of the copyright.

Hitler did have a nephew by blood https://en.wikipedia.org/wiki/William_Stuart-Houston

and I guess a few others, but dwindling https://en.wikipedia.org/wiki/Hitler_family

https://nypost.com/2018/10/08/some-of-hitlers-last-relatives...

...did they exercise it?

Rather the opposite, they disallowed anyone from printing copies