en_tn/2ki/15/30.md

Hoshea ... Elah

These are men's names. (See: rc://en/ta/man/translate/translate-names)

a conspiracy

A conspiracy is a secret plan by a group to do harm to someone or something.

He attacked him and killed him

"Hoshea attacked Pekah and killed him"

became king in his place

The phrase "in his place" is a metaphor meaning "instead of him." AT: "became king instead of Pekah" (See: rc://en/ta/man/translate/figs-metaphor)

in the twentieth year of Jotham son of Uzziah

It can be stated clearly that this is the twentieth year of his reign. AT: "In year 20 of the reign of Jotham son of Uzziah" (See: rc://en/ta/man/translate/figs-explicit and rc://en/ta/man/translate/translate-numbers)