What is the correct course of action towards a brother who is experiencing recurring financial crises, has borrowed a large sum and not repaid it, and is considering asking for more, knowing that he taunts the questioner about her financial situation despite all this?

If your brother is not in dire need of the money, then you are not obligated to lend it to him, for lending is not a duty, even if it is commendable. We advise you to lend to him if he needs the money to spend on himself and his family for permissible matters, even if he is not compelled. If you fear that he may not repay it, you can document the debt in writing and have witnesses. Advise him to be moderate in spending and diligent in earning a lawful livelihood. We advise you that your lending to him should be for the sake of Allah's pleasure and to maintain kinship ties, as the Prophet (peace and blessings be upon him) said: "Whoever wishes that his provision be expanded for him or his lifespan be extended, let him maintain his ties of kinship." And he said: "Whoever relieves a Muslim of a worldly distress, Allah will relieve him of a distress on the Day of Resurrection. And whoever eases the burden of one in difficulty, Allah will ease his burden in this world and the Hereafter." And he said: "The most beloved people to Allah are those most beneficial to people."