Who are Bnei Kini?
Malbim: They are people who dwell in tents and go from place to place; they had Shalom with Yisrael.
What is Ir ha'Temarim?
Rashi: It is Yericho (like it says in Devarim 34:3 - Radak).
Radak: It is a city near Chevron.
Malbim (3:13): It is a city near Yericho. It was forbidden to rebuild Yericho, or even to call another city Yericho (Sanhedrin 113a), therefore they called it Ir ha'Temarim.
Why did Bnei Kini leave Ir ha'Temarim?
Rashi citing Sifri: It was enacted that when the place for the Beis ha'Mikdash is chosen, the prior owner will receive the area outside Yericho; until then, it was given to the Kini. The Talmidim left to learn from Osni'el 1 (refer to 1:11:1:3).
Radak, Malbim: Perhaps they were living among Kena'anim when Yisrael conquered Chevron (near them); Yisrael called to them to separate, lest they be killed with the Kena'anim, like Sha'ul told the Kinim to separate from Amalek (Shmuel 1 15:6).
Radak: Osni'el is Yabetz; "Sofrim Yoshvei Yabetz? ha'Kinim" (Divrei ha'Yamim 1 2:55).
What is the meaning of "va'Yeshev Es ha'Am"?
Rashi: Yabetz (Divrei ha'Yamim 1 4:10), i.e. Osni'el, asked Hashem for proper Talmidim, and he received these Chasidim (Bnei Kini).
Radak: The head of Bnei Kini brought the family with him.
QUESTIONS ON RASHI
Rashi writes that Ir ha'Temarim is Yericho. It was destroyed, and it was forbidden to rebuild it (Yehoshua 6:26). Chiel rebuilt it much later, in the days of Achav (Melachim 1 16:34)!
Malbim: Refer to 1:16:2:3.
Lehoros Nasan (2:55): Nochrim rebuilt it. 1 There was no Isur to dwell there in such a case. Bnei Yisro lived there for hundreds of years!
Lehoros Nasan (2:55, citing his son R. Amram): Yonadav (from Yisro) commanded his children not to build houses (Yirmeyah 35:6,7). They lived in tents; Yehoshua forbade only fixed buildings.
It says (3:13) that Eglon took it from Yisrael. We must say that after Nochrim built it, but before Eglon, Yisrael took it. (PF)