How can one help a left-handed brother in his trade, as he is heavily indebted after taking money from some in exchange for a specific monthly payment?

Summary: You should help your brother who lost in his business by collecting part of your income to pay off his debt, or by presenting his case to charitable people. Creditors are not allowed to demand the debt from him while he is in hardship. It is better to forgive him, as Allah Almighty says: (And if there is one in hardship, then grant him respite until ease. But to remit it as charity is better for you, if you only knew). As for taking money in exchange for a loan, it is forbidden usury. However, if what he receives monthly is a portion of the capital, there is no harm in it.