A brother's stepson is not a mahram to his sisters

Question: A group of sisters who are listeners ask, saying: Your sisters in Islam, among their questions: My brother married a woman who had previously given birth to a son from another man. This son was raised in my brother's care; he was two years old at the time, and now he is twenty-five years old. May I observe hijab from him, knowing that my brother raised him and spent on him while he was an orphan?

Answer: The son mentioned is not your brother's son unless your brother's wife breastfed him from your brother's milk. If this son was breastfed by your brother's wife or your father's wife, he becomes your brother through breastfeeding. However, if he was not breastfed by your brother's wife, your father's wife, or the like, five times within the first two years, he is a stranger to you. The fact that your brother raised him does not make him a mahram to you by that. And success is from Allah.