Von does not signify royalty - it usually signified aristocracy of some level or other. Records were not destroyed to protect families - there are as many records of as many families as any where else. Many records of all sorts were destroyed during WW2 mainly because they were in the path of bombs or were destroyed in the wake of the fighting as the
Allies closed in on all sides. Prussia is not a "combination of Germany and Poland". The Kingdom of
Prussia was a part (some would say the most important!) of the
German Empire which came to an end in 1919. Therafter it was part of Germany until 1945. East
Prussia was a
Province of
Prussia and covered a large area round the Eastern end of the Baltic, stretching (roughly) from
Danzig to Lithuania, Russia and southwards into inter-war Poland. In 1945 all parts of Germany east of the Oder-Neisse rivers, which included East
Prussia, were were ceded to present day Poland with the northern half of East
Prussia being given to Russia. Maps of the old boundaries are easily available to pinpoint towns and lists giving both old and new names are also easy to find.