If there is nothing dubious about the family gatherings, it is permissible for a woman to sit with her husband’s relatives, if she is wearing complete Shar`i Hijab. However, shaking hands with a non-Mahram man is prohibited.

If a man’s stepdaughter – who is the daughter of his wife with whom he has consummated the marriage – has a stepdaughter through breastfeeding, he is a mahram to her, because the mahram relationship that is established through breastfeeding is the same as that which is established through birth.

It is permissible for a wife to shake hands with her father in-law because as soon as a man conducts a marriage contract with a woman, his father becomes a Mahram for her.