1)
Why does it say, "l'Alufeihem b'Eretz Se'ir"?
1.
Ha'amek Davar: Only in their place were they chiefs. Elsewhere, they would not have been considered chiefs. This is unlike Bnei Yishmael, who were "Nesi'im l'Umosam" (25:16) - each was proper to be Nasi over the entire nation.
