Albert Barnes Commentary Ezra 7:14

"Forasmuch as thou art sent of the king and his seven counsellors, to inquire concerning Judah and Jerusalem, according to the law of thy God which is in thy hand," — Ezra 7:14 (ASV)

Seven counselors - Herodotus relates that there were seven families pre-eminent in Persia, those of the seven conspirators against the Pseudo-Smerdis (Ezra 4:7 note); and it is reasonable to suppose that the heads of these families formed the special council of the king; the “Achaemenidae,” or royal family, being represented by the head of the branch next in succession to that of the reigning monarch (see the marginal reference).