1)
Why does it mention their tents?
1.
Radak: Yishmael came with their tents to make a long war against Yisrael, if they will not overcome them quickly.
2)
Why are some of these nations not mentioned in Divrei ha'Yamim (IT IS, 20:1)?
1.
Radak: Edom is Se'ir mentioned there; Yishmael and the other are included in Me'unim, like I explained (verse 1).
3)
Who are "Hagrim"?
1.
Radak #1: They are sons of Hagar from another husband.
2.
Radak #2: They are Bnei Keturah, according to the opinion that Keturah is Hagar.