Which Kohanim are these?
Radak: They are the Kohanim of the Beis ha'Mikdash.
Malbim: They are Kohanim of the calves.
Who is "Beis Yisrael"?
Radak #1: Shevet Yehudah; they are the primary part of Beis Yisrael.
Radak #2: It is the Sanhedrin ? they are the judges of Yisrael.
Why does he address the Kohanim, Beis Yisrael and Beis ha'Melech?
Radak: Now he comes to rebuke Yehudah, and those who could have rebuked them, i.e. the Kohanim of the Beis ha'Mikdash, in Yehudah's portion, and Beis ha'Melech. Also they should have rebuked Yisrael!
Malbim: The Kohanim enticed the nation not to go to Yerushalayim. Beis Yisrael accepted the enticement, and Beis ha'Melech heeded them ? they put guards on the road, and killed one who wanted to ascend for the festival
What Mishpat is to you?
Rashi: The judgment of afflictions is upon you, the house of Melech Yisrael.
Radak: The Kohanim, Beis Yisrael and Beis ha'Melech should have done Mishpat [against Yisrael].
Malbim: The Kohanim caused all the evil (that Yisrael did not go to Yerushalayim, and Beis ha'Melech stationed guards).
What is the meaning of "Pach Heyisem l'Mitzpah v'Reshes Perusah Al Tavor"?
Rashi: They stationed guards on these mountains to guard lest Yisrael ascend to the Mikdash for the festival. Radak ? the Midrash expounds so from "Rav Lachem me'Alos Yerushalayim" (Melachim I, 12:28). 1
Radak: You should have done Mishpat. Rather, you were a pit and stumbling block for the nation. They see that you do evil deeds, and learn from you. You are like a pit and net to snare animals and birds. So they were trapped in your evil deeds ? they do like you. It mentions Mitzpah and Tavor, for they are tall mountains in Eretz Yisrael, and trappers set their traps on them.
Radak, based on Targum Yonasan: Mitzpah is like "Tzofeh Nesaticha" (Yechezkel 3:17). He translated 'you were a stumbling block via your teaching, and like a trap set on a high mountain.
Malbim: The nation used to ascend via them to Yerushalayim. The metaphor is that by Mitzpah was a pit to trap people, and Tavor, which was wider, they spread a net to catch anyone who ascends there. Beis ha'Melech was the pit and net, for they ordered [to station guards].