What is the obligatory limit for financial assistance to an unemployed brother burdened with debts, and does this assistance include paying rent, household expenses, and loan installments?

It is obligatory to spend on a needy brother when one has the means to do so. The obligatory amount is what suffices him for food, clothing, and housing, according to what is customary. As for paying off a brother's debt, it is not obligatory. However, spending on him and paying his debt—even if not obligatory—are among the best righteous deeds, provided that this does not compromise the spender's own needs or those of his dependents.