1)
What is the meaning of "v'Karasi Alav l'Chol Harei Cherev"?
1.
Rashi: He called the sword in [the mountains] to come upon him. What sword did He call? "Cherev Ish b'Achiv."
2.
Radak: This is like b'Chol Harei or Al Kol Harei, like it says "Al Harei Yisrael Tipol" (39:4).
3.
Radak citing Targum Yonasan: I summonsed him to fall via the sword on the mountains of My nation Yisrael.
4.
Malbim: I will call to the mountains to be swords to kill and eradicate them; this is a metaphor.
2)
Why will a man's sword be on his brother?
1.
Radak: Amidst the great panic, man will kill his brother.
2.
Malbim: Edom and Yishmael will fight each other, like I explained (refer to 32:17:3:1).