Ruling on a man marrying a woman whose sister was breastfed by her mother

The letter in our hands came from Syria, from Damascus, from the listener Amin Wahali. He says: I am asking you this question, O our honorable scholars! May Allah keep you for us so that you may guide us to the right path. My question is: I have a cousin who is younger than me. Before I and this girl became [cousins], I had an older sister who was breastfed by the girl’s brother, who is much older than the girl. The boy who breastfed my sister died when he was young, and my sister is still alive and has sons and daughters. He says: The important point is that I and the girl were never breastfed by each other, but my sister and her brother, before I and the girl became [cousins], my sister was breastfed by her brother. So, is it permissible to marry my cousin? Please inform us, may Allah reward you?
Answer: There is no blame on you, O questioner, in marrying your cousin; because there is no breastfeeding or kinship between you two. Rather, the breastfeeding occurred between your older sister and her older brother from their mother, so that does not harm you. Your sister’s breastfeeding does not prevent you from marrying as long as you were not breastfed by the girl’s mother, and the girl was not breastfed by your mother, nor by your father’s wife, nor by your sisters. So, there is no blame on you in marrying the aforementioned cousin’s daughter; because there is no kinship between you and her that prevents [marriage], nor any breastfeeding that prevents [it]. As for the fact that your sister was breastfed by her mother, that does not make her forbidden to you. Yes.