Is it permissible to eat from money acquired through usury, whether its source is a brother, the wife's father, or the mother, and how can one deal with them without severing ties of kinship?

The Shari'ah commands maintaining kinship ties and promises a good reward for it. Maintaining ties with a disobedient relative or one who openly commits sins is not prohibited; rather, it may even be obligatory for the purpose of giving advice. Evidence for this is Asma bint Abi Bakr's maintaining ties with her polytheist mother.

As for food, it is permissible to eat from it if the household has another source of income besides illicit money. However, if all their income is illicit, then it is not permissible to eat from it. Loaned money is not inherently forbidden; rather, it is the usurious interest accrued from it that is forbidden. Consequently, an interest-bearing loan does not render the rest of one's money unlawful. Maintaining kinship ties with a disobedient person remains subject to an assessment of benefit and harm, except for parents, whose dutifulness is obligatory even if they are disbelievers.