Is it obligatory to maintain ties of kinship with an adopted sister who is morally corrupt and shunned by her husband's family, or is this not considered maintaining ties of kinship?

As long as the relationship is an engagement and the marriage contract has not been formalized, the suitor is a stranger to his fiancée, and he must choose a wife who is religious and of good character. The wife's family and her brothers are not kinsfolk but in-laws, and their connection is not one of kinship but rather a complement to good companionship. Relative adoption is forbidden by Islamic law, and what is called adoption today is the sponsorship of an orphan, and it does not entail the rulings of lineage. The girl mentioned is not the fiancée's sister, and her connection to her is not one of kinship. However, it is permissible to advise her and be kind to her, without assisting her in disobedience. Upon marriage, the husband must safeguard his wife and protect her religion and morals from bad companions.