He also walked in the way of the house of Ahab: See the comments on the very similar expression in verse 18.

And did what was evil in the sight of the LORD: As in verse 18, it will be misleading in most languages to use the conjunction and between the previous statement and the one here. This second statement is merely an elaboration of the first one.

As the house of Ahab had done: See the comments on verse 18.

He was son-in-law to the house of Ahab: The Hebrew word rendered son-in-law occurs twenty times in the Old Testament (sometimes translated “bridegroom”). Normally the word is used to express a relationship to a specifically named person (Neh 6.18; 13.28), a person referred to by title (1 Sam 18.18), a person referred to by place of origin (Jdg 15.6), or a person referred to by a possessive pronoun (for example, “his son-in-law” in Jdg 19.5). Here, however, it is not related to an individual. Ahaziah is said to be the son-in-law to the house of Ahab. The Hebrew word may also mean “family relative” and not just “son-in-law.” Most modern versions take it here to have a more general meaning like “related by marriage”; for example, the whole clause has been translated “he was connected with that house by marriage” (Revised English Bible), “he was related to them by marriage” (New American Bible), and “to whom he was related by marriage” (New Jerusalem Bible).

Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on 1-2 Kings, Volume 2. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here .