What is the ruling on a wife continuing to wear a head covering in front of her husband's family and adhering to full, lawful hijab, even if they mock her on the pretext that hijab is unnecessary in family gatherings? And how can she convince them of the benefits of lawful adherence while avoiding offending them? And are the sons of the husband's brother or sister considered mahrams? And what is the ruling on shaking hands with them if this custom is widespread in the family?

The sons of the husband's brother and sister are not mahrams; rather, they are strangers from whom one must be more cautious. The Prophet, peace and blessings be upon him, likened them to death due to the serious nature of their fitna (temptation/trial) and their ability to reach and be in seclusion with a woman, unlike other strangers. It is permissible for a woman to sit with them if she is wearing the legal hijab (definition), as long as there is no suspicion in the sitting. However, it is forbidden for her to be in seclusion with any of them or to shake their hands, based on the Prophet's saying, "Indeed, I do not shake hands with women."