Complex sentence: They are not mentioned in any other historical source, and since "Cäğfär Taríxı" is believed to be a forgery created by the NKVD, the historiocity of these two kings is highly suspect.
Split into simpler sentences: They are not mentioned in any other historical source. Since "Cäğfär Taríxı" is believed to be a forgery created by the NKVD, the historiocity of these two kings is highly suspect.