Translation:The sister of my spouse is my sister-in-law.
Well, many do use sviger-"insert family member", even when not married, some even in a fresh relationship, but it is not correct. It would at the very least be an underlying hint that this is a relationship going for the long run. Some also like to use it to display trust or affection. But it is correvtly used only when married. Also, one often shortens it if it's obvious who you are talking about, just to "svigers".
And if you would like to talk about any member if your spouses family, you just add "svigers". "svigeroldemor", "svigerstefar" "svigertremenning".
Do I have to be consistent with where I put the min (before or after the noun)? I wrote down "svigerinnen min" instead of "min svigerinne", which is correct on its own, but I guess because it was already "min ektefelle" (possessive pronoun before the noun) I have to be consistent and put min before instead of after the second noun too? Or is it just because the audio was one way, that the other way was not accepted?