Exactly so! The information provided so far is all correct!
Thumbs up for ''Amene'' as well as ''Poppy Amelia Sevina'' for taking the time to thoroughly explain. : )
Well, I'd like just to add that that is true for all the 'in-law's'. In other words - in English, the term 'in-law' is transferred to the relation or correlation of all the supposed members of one's spouse's family.
GLOSSARY - spouse: formal term used when referring to someone's husband or wife.
In case of any question or doubt regarding this comment, please, feel free to leave me a message.
Hope I've been a bit of a help. : )