stepfather

Asalamu Alakum respected scholar, i would like to know wheather or not my stepdad is my mahram. I have grown up with him ever since i was 5 years old when my mother married him. If he is not my mahram does this mean i have committed a great sin not covering myself (hijab) infront of him? And do I have to listen to everything he commands from me seeing that he treats me like his own daughter?Jakuallah

Dear scholars, As-Salamu `alaykum. This question is about spouses who have children each from a previous marriage; the man has two sons while the woman has two girls. The girls are about to attain puberty (about 12 & 10) and the boys have attained maturity. The question is: Should the girls wear Hijab in front of their stepfather after reaching the age of puberty? And should they do this in front of their stepbrothers? Jazakum Allah khayran.