Is it permissible to accept money from a second wife if its origin is an interest-based loan from a bank, knowing that the husband's financial capabilities do not allow for supporting two families?

Borrowing with usury is one of the gravest major sins. However, your benefit from this woman's money is permissible because she acquired the money through a loan. She should be advised to repent from borrowing with usury, while also noting that Islamic law does not condone a relationship between a man and a woman before marriage.