Is it permissible to borrow from someone whose money is in an usurious bank or whose money is unlawful? And is it permissible to take money to work with it and give its owner a fixed amount as a guaranteed profit? And what is the legitimate way to take money for investment while returning the profits? And is it permissible to give the wife a fixed monthly amount from this money, even if it is lost, to appease her, if the money will return to the children?

Borrowing from someone whose entire wealth is unlawful is impermissible. If some of it is unlawful and some is lawful, then it is disliked. It is permissible for him to give you a portion of his wealth for trading on the basis of Mudarabah (profit-sharing) according to the Sharia-compliant conditions. If the owner of the wealth is your wife and you wish to give her a fixed monthly amount from her share of the profit, there is no harm in that. She has the right to the amount if she fulfills her share, and you may waive the rest for her without a condition in the contract.