The German Empire and Kingdom of Prussia were abolished in 1918. The current head of the former ruling House of Hohenzollern is Georg Friedrich, Prince of Prussia. The Law of Succession used is Agnatic Primogeniture.
The Head of the House of Hohenzollern is styled His Imperial and Royal Highness the Prince of Prussia. The house is smaller now than it was in 1918 because after the monarchy was deposed, many princes married morganatically, excluding their descendants from the list of dynastic princes. For example, the two eldest sons of Louis Ferdinand, Prince of Prussia married morganatically.
Members of this family compose the Prussian Royal Family. There was no German Imperial Family as the only individuals with German imperial titles were the emperor, his consort, empresses dowager, the crown prince and the crown princess. There were no Princes of Germany, only princes of Prussia.