“Mortuos Antiquos” eh… maybe, take your pick I guess, the germanic peasants and lords are the ones naming everything, and the saxon/celt/roman undead seem unlikely to provide answers as to their origin.
Based off that; “Alten-Toten” seems a bit more likely to me and has a ring to it, but I’m an ignorant Englishman and either one of those titles might sound totally lame to someone who knows the language lol.