Is it permissible to stay in the house of a brother who prays, he and his wife, but the brother works with a secular party, knowing that the questioner is committed to Islam and works with his brother in the internet field?

Working with secular individuals within permissible limits is allowed, but it is better to seek another alternative. However, working with them in what is prohibited, or what assists them in it, is not permissible. If your brother believes in secular thought or works to establish its principles, you must advise him and explain the danger of this principle and its contradiction to Islam. There is no harm in living with him in one house, as long as it does not lead to a Sharia-prohibited matter.