The Definition of a Woman's Mahram and Its Conditions

Question:
A questioner says, may Allah preserve you: Who is the mahram of a woman? And is it permissible for a woman to travel with her sister's husband, along with her sister and her young sister who is seven years old, out of necessity?

Answer:
The mahram of a woman is one who is forbidden to her by lineage or by a cause of lineage, such as her brother, her brother's son, her son, her son's son, her father, and her grandfather. It is also one who is forbidden to her by a cause, such as her daughter's husband by affinity, or by breastfeeding. Breastfeeding is one of the causes that creates prohibition, and the breastfed child becomes a son to the wet nurse and a brother to her other children. This is the cause.
It is required that the mahram be an adult and of sound mind. It is required that the mahram be an adult, so one who has not reached puberty is not a mahram. And he must be of sound mind, so one of the foolish who do not have reason is not a mahram, in order that he can take care of her, protect her, fulfill her rights during travel, and safeguard her. Her husband's brother is not a mahram for her, so it is not permissible for her to travel with her sister and her sister's husband, because she would be traveling without a mahram. The Prophet (peace and blessings be upon him) said: It is not permissible for a woman who believes in Allah and the Last Day to travel except with a mahram. Yes.

The presenter:
May Allah reward you,