What is the ruling on the money earned by my brother from selling food products and cigarettes, from which he gives to our mother to buy her medicine and necessities, as well as the food that our mother buys with this money and from which the questioner eats, or the money that my brother gives to the questioner for transportation, knowing that this money is our mother's only source of income? And what is the expiation for that, if there is sin?

As long as your brother sells food products, the origin of his money is lawful. The unlawful earnings he acquires from selling cigarettes do not render all of his money unlawful, nor do they prevent you from benefiting from it. Dealing with someone whose money is mixed [lawful and unlawful] is permissible, especially if the majority of their wealth is lawful. Therefore, there is no sin upon your mother or you in benefiting from your brother’s money. However, you should advise him and explain the impermissibility of selling cigarettes.