Here God calls a man having sex with his son's wife a "perversion", a serious sin. See how you translated "perversion" in [Leviticus 18:23](../18/23.md).
The word "blood" here is a metonym for the guilt of putting someone to a violent death. See how you translated similar words in [Leviticus 19:9](../19/09.md). Alternate translation: "the guilt for their violent death is theirs alone" (See: [[rc://en/ta/man/jit/figs-metonymy]])