“Inuit” is a plural noun! One need not add the English plural morpheme -s to it because it already has the Inuktut plural morpheme -it! The singular form is actually “Inuk.” A common Canadian and Greenlandic dual form is “Inuuk.”
There are grammatical dual as well as singular and plural nouns and pronouns in most of the Inuit-Yuit-Unangan languages, excluding Sireniki Yupik†, Kalaallisut, and Tunumiisut; Unangam Tunuu also used the dual more often prior to the 1950s.
In northern Iñupiatun, one person is an iñuk; two people are iññuk; three or more are iñuich. In Yugtun: yuk; yuuk; yuit. In Eastern Unangam Tunuu: anĝaĝix̂, anĝaĝix, anĝaĝin. A possible Unangax̂ language cognate of iñuk, inuk, yuk, cuk, cug, suk, and yuuk is suganĝix̂ “young person.”
As for three examples of Alaskan ethnonyms in the singular, dual, and plural:—
Siḷaliñiġmiutun and Malimiutun: singular Iñupiaq; dual Iñupiak; plural Iñupiat.
Northern Central Alaskan Yugtun: singular Yup’ik; dual Yupiik; plural Yupiit.
Unangam Tunuu: singular Unangax̂; dual Unangax; plural Unangan or Unangas (Attu†).