Is a wife obligated to remove her hijab, which she started wearing years after her marriage, at the request of her husband and his threat of divorce, especially when there are four children and she is unable to work?

It is impermissible for your husband to order you to remove your hijab, and it is impermissible for you to obey him in this matter, due to the Prophet's (peace be upon him) saying: "Obedience is only in what is good and right." This is a grave disobedience, as Allah Almighty and His Messenger have commanded it. It is not permissible for you to obey him in this, even if it leads to divorce. Rather, you should remind him of Allah and invite him with wisdom and good counsel. If he divorces you, Allah will compensate you, and provide for you and your children, for "whoever fears Allah, He will make for him a way out and will provide for him from where he does not expect."