Is the work of a brother in a government company for cultivating and selling barley permissible, knowing that there are companies that buy it for use in manufacturing alcohol, and is the salary earned from this work permissible or forbidden?

There is no objection to your brother working as an accountant at the aforementioned company, as his work does not involve assisting in the forbidden, and he is allowed to benefit from his salary. The company's sale of barley is not forbidden unless it sells it to someone who will use it for forbidden purposes, and your brother's field of work has no connection to this matter.