Mike, I most certainly could lighten the picture up. But it would be difficult for me to retain an outwardly dignified composure.

Firstly, your friends have been misinforming you.
And I wonder why. The Firearms Office (on county or city level) have NOT misinformed them; that is for sure. So, why did they choose to tell you wrongly, and to mislead you? Shame it was, most likely.

The firearms law provisions on heirs and legatees of firearms have not changed substantially since 1976 (49 years), now to be found in par. 20 WaffG. Only the consequences have been made more cumbersome / burdensome. But you still will get your inheritance FAC (Erben-Waffenbesitzkarte) if you request it within the legal application deadline, only the actual possession of ammunition is no longer simply inheritable since 2003. And the side costs (blocking system, and acquisition of a new vault at today's prescribed standard) have risen very significantly.

Secondly, this specific calibre combination in a post-war Heym drilling is practically unsellable at all, although I do very well understand the dusty and time-forlorn considerations that once were behind it. No dealer or gunsmith anywhere in Germany will even take it in commission or in trade. Sad, but starkly true.
An ordinary 16-16-7x57R drilling might eventually find a new home for a low price (300 to 600 €, depending upon condition). This one? Emphatically NOT!

Carcano