What do the respected scholars say regarding this matter: My mother breastfed a girl who also has other sisters whom my mother did not breastfeed. Can my elder brother marry any of the sisters of that girl?
The girl whom the questioner’s mother breastfed during the nursing period cannot be married by the questioner or any of his other brothers. However, it is permissible and valid according to Shariah for the questioner’s elder brother to marry any one of the other sisters of that girl, provided that no other cause of prohibition exists.
ففی اللباب في شرح الكتاب: (ويجوز أن يتزوج الرجل بأخت أخيه من الرضاع، كما يجوز أن يتزوج بأخت أخيه من النسب اھ (3/ 33) واللہ اعلم بالصواب