Q. Are step-siblings Mahrams to each other? Is there a difference if they share the same parents or not? What is the ruling of Hijaab in front of them?
A.Siblings who the share the same mother (Uterine siblings), for e.g. one’s mother married two husbands and she had children from both husbands, or siblings who share the same father (Consanguine siblings), for e.g. one’s father married two wives and he had children from both wives, fall under ones unmarriageable kin (Mahrams). Observing the laws of Hijaab between them is not necessary.
On the other hand, siblings who don’t share the same parent but are from previous marriages, for e.g. one’s mother/father married a second husband/wife who had sons/daughters from a previous marriage fall under ones marriageable kin (non-Mahrams). Observing the laws of Hijaab between them is necessary. (Badaai-us-Sanaai 2/257)
Allah Ta’ala Knows Best
Mufti Ismaeel Bassa