Why is Cheshbon listed first?
Malbim: It screamed first, for the enemy came to there first.
What is "Eglas Shelishiyah"?
Rashi: It is a strong country, [Rashi Yeshayah 15:5 - like a calf born third to its mother].
Radak: Eglas is like Eglah. The Tov is in place of a Hei. The same applies to "v'So'avas l'Adam Letz" (Mishlei 24:9), "Af Gilas v'Ranen" (Yeshayah 35:2), "Al Titni Fugas Lach" (Eichah 2:18) and similar verses. Shelishis is big, or three years old 1 , for that is good. So Mo'av was full of all good when the hunger came.
Radak citing Targum Yonasan: A third grown calf.
Malbim: The circle (group) of Giborim and officers of Mo'av. 2
If so, all agree that it is called Parah, and not Eglah! R. Eliezer says that a one-year old is called an Eglah, and a two-year old is called a Parah (for Eglah Arufah and Parah Adumah). R. Meir says that a two-year old is called an Eglah, and a three-year old is called a Parah (Parah 1:1)! (PF)
Perhaps the text should say "Ra'ah" (evil), and not Ra'av. (PF)
What is "Nimrim"?
Radak #1: It is the name of a river.
Radak #2: It is the name of a place in Eretz Mo'av.
Malbim: It is a port where ships embarked and arrived, and a great business market.
Will they truly be desolate?
Radak: All the residents will be killed or will flee. Since there are no residents, it is as if there is no water or vegetation.