I doubt very much that in their dealings with the new republic that members of the formerly-reigning Imperial Family would have ever been able to use the name 'Österreich' ('Austria'), particularly paired with the enactment of a ban on the use of prepositions in civil names. I think that the use of various forms of Habsburg-Lorraine by the wider dynasty is a unifying measure, particularly also when their former realms are now a number of different countries and perhaps just 'Austria' would be alienating now. However, when Crown Prince Otto's daughter Archduchess Gabriela was born in Luxembourg in 1956 the name on her birth certificate was 'von Österreich-Ungarn' ('of Austria-Hungary').

The members of the formerly reigning German dynasties can style themselves any which way that they want; titles have been converted into surnames (differentiated by gender) but confer no legal privileges, etc, whatsoever as nobility is not legally recognized in the federal republic having been abolished under republican laws following the end of the monarchies. Bavarian royals use the surname 'Prinz(essin) von Bayern', the head of the house uses the surname 'Hezog von Bayern', and a junior branch maintains the surname 'Herzog(in) in Bayern'. There is no reason for them to use any form of 'Wittelsbach' in a civil name because they were never habitually called "of Wittelsbach" since the Bavarian titles were their highest consistently used ones.