Is it permissible for a sister to benefit from the usurious bank interest of her brother to meet her dire needs and grow her business?

It is not permissible to deposit money in usurious banks, as it constitutes cooperation in sin and transgression, unless a Muslim is compelled to do so out of fear of theft and finds no alternative, provided that the account does not generate usurious interest.

If usurious interest accrues, it is not permissible to own it. Rather, it must be spent on charitable causes as a means of getting rid of it, not as an act of drawing closer to Allah, such as for public welfare or for the poor and needy. The ruling on spending it on relatives has been clarified in Fatwa (definition) No. 39269.