Are uterine siblings (children from one mother) Mahrams to each other? 

Q. I Have a son and a daughter. My son was born from my first marriage and my daughter was born from my second marriage. They are now Baaligh. Is my son from my first marriage a Mahram to my daughter from my second marriage?

A. Uterine siblings (children from one mother), irrespective if the mother bore them through different husbands or marriages, are considered to be Mahrams (non-strangers) to one another. Accordingly, your son and daughter (uterine siblings) are Mahrams to one another.

Allah Ta’ala Knows Best

Mufti Ismaeel Bassa

themufti.com