Are the wives of the daughters of a brother's son among the mahram (forbidden to marry)?

Question:
You also say: My brother's son has married daughters. Are their wives mahram to me?

Answer:
As mentioned earlier, no. The wives of a brother's daughters and a sister's daughters are not mahram. As stated, the mahram are the husband of a daughter, the husband of a daughter's daughter, the husband of a son's daughter—meaning the daughter of a woman's son—and so on down the line. These are the mahram. Likewise, the husband of a mother is a mahram to her daughter if he has had sexual relations with her, meaning if the mother has been penetrated, due to the saying of the Exalted: [Surat al-Nisa: 23]. Therefore, penetration: sexual intercourse. So, the husband of her mother is a mahram to her if he has had sexual relations with her mother, even if she was not raised in his household. The description of being in the household is a general characteristic. Likewise, the husband of her maternal or paternal grandmother is also a mahram to her if he has had sexual relations with the mother. Yes.