Assalamualaikum Wr. Wb.
Thank you for taking the time to read my question, for I have searched and read many answers on your Fatwa Center regarding step-sons and hijab, but I believe I still have one item that makes mine a unique situation.
My 10-year-old step son used to live with us, until he decided to live with his birth mother and teenage siblings. We soon learned that he has lived the life of a kufar with exposure to sex, drugs and drinking. He has since told his father that he no longer wishes to practice Islam and understands what it means to be kufar, but he would rather live with his mom and live life their way.
Well, he comes to visit every two weeks and the house is odd. I don't feel comfortable letting down my guard or even my hijab around him anymore because his innocence is gone. Not to mention he no longer looks at me as a mother.
My intuition to keep hijab has not pleased my husband for he feels I have created a rift. Therefore, my question is...does the ruling of hijab still apply in the instance of a kufar step-son?
Jazakallah Khair for your time and consideration.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

We have already issued Fatwa 88233 clarifying that the step-son is an eternal Mahram to the woman; Allaah Says (what means): {And do not marry those [women] whom your fathers married.}[Quran 4:22]

This is the principle, but if there is something suspicious between the boy and the wife of his father, then she is obliged to wear Hijab in front of him, and not allow him to be in seclusion with her; these rulings apply to any other male Mahram of hers.

On one hand, we advise the father to be soft with this boy and endeavour to influence him, and this matter is possible especially that he is at this age and might not yet reached the age of puberty. On the other hand, the father should be firm with him. If he can travel with him in order to reside (with his family) in a Muslim country, then he should do so. Residing in a non-Muslim country is a reason for such temptations in general.

The following matters should be mentioned:

1-    There is no difference between a Muslim Mahram and a non-Muslim Mahram in regard to the permissibility of shaking hands, staying in seclusion and travelling, unless he believes that it is permissible to marry Mahram women or that he is a cuckold, in which case the woman should be careful of him and treat him as a non-Mahram.

2-    The jurists differed in opinion about the apostasy of a boy who reached the age of distinction; some of them are of the view that his apostasy is possible whereas some others consider that it is not possible because he is not yet obliged to perform religious obligations [due to his young age].

Allaah Knows best.