Ruling on marriage to the sister of a person with whom he was breastfed
Question

                What is the ruling on marriage to the sister of one’s sister through breastfeeding?.
Praise be to Allah.If a man has a sister 
    through breastfeeding, who was breastfed by his mother, or was breastfed 
    along with him by another woman, he may marry her sister, because the mahram 
    relationship here is limited only to the one who was breastfed, and not her 
    sisters. 
But if he was breastfed by 
    the mother of the girl, then he is a brother to the girl and to all her 
    sisters, so it is not permissible for him to marry any of them. 
And Allaah knows best.