Do not be sexually intimate with a woman and her son’s daughter
“Her son’s daughter” Vayikra 18:17
Do not be sexually intimate with a woman and her daughter’s daughter
“Her daughter’s daughter you shall not take” Vayikra 18:17
From the time one marries a woman her mother, her mother’s mother, her father’s mother become forbidden to him including her daughter, her daughter’s daughter and son’s daughter.
Regarding these 6 women the penalty is death by burning for sexual intimacy during his wife’s lifetime-whether he was intimate with them with the intention of marriage or immorality.
If he was sexually intimate with any of them after his wife’s death the penalty is Divine severance and if unwittingly a sin offering is required.
It is specifically when a person marries a woman that her relatives become forbidden to him.
If he had immoral relations with a woman it is not forbidden to marry her relatives.
The Sages forbade marrying these relatives of the woman with whom he had immoral relations.
If he took them he need not divorce her.
The secondary sexual relations prohibited by the Scribes are
For a woman and her son’s daughter
the daughter of one’s wife’s son’s son
the mother of his wife’s mother’s father
the mother of his wife’s father’s father.
For a woman and her daughter’s daughter
the daughter of one’s wife’s daughter’s daughter
the mother of his wife’s mother’s mother
This applies in all places at all times.