Edom disposed of the Horites, Moav and Ammon the Rephaim/Emim/Zamzumim etc. (Devarim 2:10-12)
What sons of Noach are these peoples descended from?
If they’re giants (Emim/Zamzumim), are they presumed to be descended from Og?
Chori: Shabbos 85a identifies the Chori with the Chivi, the nation listed in Bereishis 10:17 as being the son of Canaan, himself a son of Cham.
Moav and Amon: Bereishis 19:31-38 records that they are the sons of Lot by way of his daughters. Lot‘s father Charan was Terach’s son, Avraham’s brother (Genesis 11:27). All of them are descendants of Shem (ibid. v. 10-26).
Refaim: This is indeed the nation of Og (Rashi to Bereishis 15:20, from Devarim 3:13). Og himself, if we are to take the Midrashim literally, is a survivor of pre-Noachide times (Niddah 61a, Zevachim 113b), a descendant of the Nephilim (Rashi to Bereishis 14:13, from Bereishis Rabbah 42:8).
As you allude to in your question, this was the nation the Moavim called the Eimim (Devarim 2:11) and which the Amonim called the Zamzumim (ibid. v. 20). Note that Bereishis 14:5 lists the Eimim and Zamzumim (see Rashi ad. loc. who translates the name Zuzim in the passuk as Zamzumim) as living in separate cities, so perhaps these are different parts of one nation, rather than being one group called multiple names.