I wondered why, in P.Theroff's site, Pr. Xelal's line descendants were preceeded by Pr./Pss with a ? Question Mark.
I guess that's the explanation. They are not Zog's descendants, so they are not "proper" princes and princesses.
Between 1928 and 1939 (and also later on in exile) certain nephews and nieces (especially Tati and Princess Adile's children) were known as princes and princesses but this was sort of a courtesy and these titles were neither legally granted by the King (he was not allowed to grant titles) nor legal from the point of the Constitution. I guess that is how this slight confusion about these "titles" started.