Can a woman marry her step daughter off with her real brother?
In the name of Allah, the most Beneficent, the most Merciful.
There are two ways to look at this question. If the stepmother breastfed the daughter within 30 months of the child’s birth, it will not be permissible for the daughter to marry her stepmothers real brother as he will become the maternal uncle of this daughter. (Hidayah p.351 v.2)
In a lengthy hadith narrated by Saaidah Aaisha Radiallahu Anha the Prophet of Allah Sallallahu Alahi Wasalam said, “…Suckling makes unlawful which are unlawful according to parturition.” (Sahih Bukhari p.763 v.2)
However, if the stepmother did not breastfeed the daughter it will be permissible for the daughter to marry the real brother of the stepmother.
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham.