This can be stated in active form. Alternate translation: "The enemy army will devastate Moab and attack its cities" (See: [[rc://en/ta/man/translate/figs-activepassive]])
The best men of Moab going to battle and being killed is spoken of as if they were animals taken to a place to be slaughtered. Alternate translation: "their fine young men will all be slaughtered" or "the enemy army will kill all of the finest men of Moab" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "king" refers to Yahweh. This can be stated in first person. See how you translated this in [Jeremiah 46:18](../46/18.md). Alternate translation: "This is what I, the king, declare" (See: [[rc://en/ta/man/translate/figs-123person]])