Is the husband of one's sister considered among the kinfolk whom one is obligated to maintain ties with, and what is the ruling on shunning the husband's sister or limiting contact with her to phone calls, due to the niqabi woman's unwillingness to meet her husband, who deliberately saw her and is bothered by her niqab?

First: Wearing the niqab is permissible and obligatory. There is no sin upon you if your sister's husband sees you unintentionally; the sin is upon him if he deliberately looks.

Second: The sister's husband is a stranger to her, not a mahram (definition). Therefore, it is obligatory to cover from him, and it is forbidden to shake hands with him or to be alone with him. It is not necessary to go to his house or to contact him. It is permissible to sit with him while wearing your niqab and in the presence of a mahram if suspicion is absent and temptation is secure. A piece of advice: do not sit with him if he deliberately looks at you when you are not wearing hijab (definition).

Third: This should not affect your relationship with your sister. You must maintain ties with her, and you can visit her at times when her husband is not present.

Fourth: It is not obligatory to sit with your sister's husband when he visits you. The important thing is to adhere to covering, modesty, and chastity.