Is the woman considered sinful for living with her brother who deals in usury, and must she leave the house if she finds a job?

Usurious gains are money forbidden by Islamic law. Your brother must repent to Allah and withdraw his money from the usurious bank, and dispose of the interest by spending it on general public welfare for Muslims or on the poor and needy. He is not permitted to benefit from it personally. As for you, you may take from these interest gains to the extent of your need if you have no other money. However, if you find lawful work, you are no longer permitted to take from it thereafter. Residing in your brother's house, for which he pays rent from usurious gains, is permissible, because the forbidden aspect is attached to the earner's liability, not to the house itself. This ruling applies if all your brother's money is from usurious gains. However, if it is mixed with lawful money, the ruling differs.