Shayegan, M. Rahim. 2012. Aspects of History and Epic in Ancient Iran: From Gaumāta to Wahnām. Hellenic Studies Series 52. Washington, DC: Center for Hellenic Studies. http://nrs.harvard.edu/urn-3:hul.ebook:CHS_ShayeganM.Aspects_of_History_and_Epic_in_Ancient_Iran.2012.
Chapter 1. The Sources
Old Persian Epigraphy: The Bisotun Inscription
As a result of this claim, the people rose up against Cambyses and went over to Gaumāta, thus enabling him to take possession of the empire:
Following Cambyses’ death, nobody dared to contest Gaumāta’s seizure of power, for he would put to death all those who had previously known Bardiya. Darius, helped by a few followers, confronted Gaumāta and finally killed him in Media:
Main Classical Sources
Patizeithēs’ own brother Smerdis resembled the defunct prince Smerdis to such a degree that he could be substituted for the prince without the people recognizing this subterfuge. Therefore, Patizeithēs established his brother on the throne and proclaimed his accession throughout the empire:
In response to this, Darius and a handful of his companions fomented a coup d’état and killed the two magi in their palace:
Justin’s Epitome of Pompeius Trogus
Nobody was informed of this substitution, except the closest members of Cambyses’ entourage: Artasyras, Bagapatēs, and Izabatēs.  Five years after the substitution, the queen mother Amytis discovered the truth and demanded the head of the magus; upon being refused by Cambyses, she took poison and damned her older son before dying. 
|Kingmaker + Puppet-king
Patizeithēs | Smerdis +
Cometes | Oropastes
Dionysius of Miletus, Hellanicus of Lesbos, and Aeschylus
Since Cambyses had merely one brother—on which point all of our sources, despite otherwise considerable variations, seem to agree—the question re-mains as to the reason for the duplication of the singleton in this scholion. Un-doubtedly, the story of the two magian brethren in the accounts of Herodotus and Trogus ought to have colored the scholion attributed to Hellanicus. It is very likely that Hellanicus himself had retained only the story of two brothers, Merphis and Maraphis, with the former being fashioned in analogy with the name of the usurper as it appears in Aeschylus, as Μάρδος, or in Herodotus, as Σμέρδις. The identification by the later scholiasts of one of the magian brothers with Bardiya, on account of his perfect resemblance with the latter, probably led to the two magians jointly becoming brethren to Cambyses. Thus, we ought to assume that, aside from Herodotus and Trogus’ source, Hellanicus also knew of two usurper brothers, although no word of their being magi is mentioned.
πέμπτος δὲ Μάρδος ἦρξεν αἰσχύνη πάτραι
θρόνοισί τ᾿ ἀρχαίοισι· τὸν δὲ σὺν δόλωι
Ἀρταφρένης ἔκτεινεν ἐσθλὸς ἐν δόμοις
ξὺν ἀνδράσιν φίλοισιν οἷς τόδ᾿ ἦν χρέος.
ἓκτος δὲ Μάραφις· ἕβδομος δ᾿ Ἀρταφρένης
κἀγὼ· πάλου τ᾿ ἔκυρσα τοῦπερ ἤθελον
κἀπεστράτευσα πολλὰ σὺν πολλῶι στρατῶι. 
Mardos governed as fifth, a shame to his native land
and to the ancient throne; but through a cunning plot
the brave/fortunate Artaphrenēs slew him in his chambers,
together with friends, whose duty this was.
Sixth (was) Maraphis; and seventh (it was between) Artaphrenēs
and me  ; I obtained the lot I desired,
and made many wars with a mighty force.
Minor, Late Antique, and Syriac Sources
Noteworthy in this testimony is the metamorphosis of Darius’ helpers, the Seven (conspirators), into seven magi, whom Darius would eventually eliminate.
The Syriac Apocalypse of Daniel
Comparison of Sources
|Names of Usurpers/Rulers||Smerdis Patizeithēs||Oropastes Cometes||Merphis Maraphis||Mardos Maraphis|
|Relations & Functions||= 2 magian brothers||= 2 magian brothers||= 2 brothers of Cambyses||= 2 rulers|