Sherira ben Hanina has written:

'The iggeres of Ray Sherira Gaon' -- subject- s -: History, Mishnah, Talmud, Tannaim

'The Iggeres of Rav Sherira Gaon' -- subject- s -: Amoraim, Geonim, History, Mishnah, Saboraim, Talmud, Tannaim

Arthur Spanier has written:

'Die Toseftaperiode in der tannaitischen Literatur' -- subject(s): Tannaim, Tosefta

Shulamis Frieman has written:

'Who's who in the Talmud' -- subject(s): Amoraim, Biography, Dictionaries, Talmud, Tannaim

The Herodian kings were all in the latter century of the Second Temple era. The Jewish sages of the time were called Tannaim, sages of the Mishna. Hillel was active at that time.

No, the singular forms are the aramaic tanna/amora.

However, they have been imported back into Hebrew and given the Hebrew plural suffix.

As a result they resemble dual forms, but are not.