User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-3965848-20150524093458/@comment-3965848-20150525190120

I think the accurate term for non-blood sibling's whose parents marry each other is "step" not in-law.

Step siblings being together isn't as bad, but were talking two family members who are blood related (such as sister's, female cousins and/or mother and daughter) being with the same guy, that's incest even if the guy is not related.