A woman traveling for 'Umrah with her sister and her sister's husband, and the explanation of the mahram

Question:
This questioner says: Is it permissible for a woman to perform 'Umrah with her sister and her sister's husband, such that her sister's husband would be her mahram?

Answer:
He is not a mahram for her, and it is not permissible for her to travel with him. Even if her sister were with him as a companion for both of them, he is not a mahram for her, and it is not permissible for her to travel except with a mahram, as in the hadith: except with a mahram. Yes. The mahram is one who is forbidden to her by lineage, such as her brother, her paternal uncle, or her maternal uncle, or by a permissible cause, such as breastfeeding or being a son-in-law, like her husband's father or her husband's son. This is a mahram for her, a son-in-law. Yes.

The presenter:
May Allah reward you,