As for Nganasan, see A Grammar of Nganasan, 2018, BRILL, by Beáta Wagner-Nagy. In short, it says that the relative clauses are usually participial constructions, the adverbial clauses stick to the usual Nganasan SOV word order.
The same goes about Selkup, if it it is really a clause, the word order is SOV. The only grammar that deals with the Selkup subordinate clauses I have is the 1935 Soviet Селькупский (остяко-самоедский) язык. часть 1 - Селькупская грамматика by Прокофьев Г. Н. (“The Selkup (Ostyak-Samoyed) Language. Part 1 – A Selkup Grammar”, 1935, Prokofyev G. N.), §141 pp. 98–100, in Russian and Selkup in the then Latin-based orthography. The author maintains that subordinate clauses are pretty rare in Selkup and that participial constructions are more preferred.
Unfortunately, I have no data on the other two languages you have mentioned.