Here "turn away" is an idiom that means he no longer obeyed Yahweh. AT: "stopped obeying Yahweh" or "started to disobey Yahweh" (See: [[rc://en/ta/man/translate/figs-idiom]])
The text does not state to whom "they" refers. Retain the generic "they" in your translation if possible.
# make a conspiracy against him
The abstract noun "conspiracy" can be stated as an action. AT: "conspire against him" or "plot against him" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
# Lachish
a city in Judah (See: [[rc://en/ta/man/translate/translate-names]])