Once again the verb takes
(yiqqǎḥ) suggests that these individuals had married each other or they were living as husband and wife. The punishment for both the man and his sister is that they shall be cut off from the nation of Israel. This signifies that they shall be excommunicated from the community.
17 “If a man takes his sister, a daughter of his father or a daughter of his mother, and sees her nakedness, and she sees his nakedness, it is a disgrace, and they shall be cut off in the sight of the children of their people. He has uncovered his sister’s nakedness, and he shall bear his iniquity.