What is the ruling on someone who manages a company owned by individuals who have dealt with usurious banks, and what are the limits of his responsibility for money from which he owns nothing but his salary, and when is he responsible for the usury that may be attached to this money?

Taking usurious loans does not prevent working with those people and managing their company, as long as its field of work is not forbidden. The Prophet, peace and blessings be upon him, traded with the Jews, and they were devourers of usury, and he died with his shield mortgaged to a Jew. There is no harm in dealing with them and working with them in what is permissible, even if some of their earnings are forbidden. However, it is not permissible for the employee to perform any forbidden work in the company.