Step brother from Zina

Question:

Many years ago when I was married to my ex husband, he had a relationship with a non Muslim woman which resulted in them having a son at the time. He and myself had young daughters. Alhamdu lillah the woman shortly after her son’s birth became Muslim, he then married her and she became my co-wife, and our children grew up together as brother and sisters. However since they reached puberty, I sought advice and was told that he is not a mahram to my daughters and that they should cover in front of him.Is this correct? If yes, should they not sit and chat with him, be alone with him etc?

 Shaykh Walid Boghdady:                                                                                                                                                                                                 

Yes, he is their brother and he is their mahram. Yet, as a general advice to everyone, make sure that your daughters, even if they are not requested to wear hijab, should wear decent clothes in front of their brothers and avoid tight clothing. This is something requested when girls are with their mahram.