What is the ruling on a stepmother who prevents her deceased husband's daughter from visiting her biological mother, and who has priority in care: the stepmother or the biological mother? And does the husband incur the sin of severing ties of kinship in this case?

The stepmother has no right to prevent the husband's daughter from visiting her mother, as this constitutes severing ties of kinship and inciting disobedience to the mother, which is forbidden and a major sin. The mother's right is great, and it is obligatory to honor her and forbidden to sever ties with her, even if she is abusive. As for the stepmother, she does not have a special right like parents and close relatives, although kindness to her is encouraged. The husband must order his wife to honor her parents and maintain ties with her relatives, for it is his duty and guardianship to obligate her to perform duties and prevent her from forbidden acts.