Breastfeeding does not extend from the infant to his blood relatives

Question: (F) was breastfed by (M)'s mother with a complete breastfeeding. Since the mentioned (F) has an older sister, is (M) a mahram (a relative one may not marry) to her or not? If the answer is no, is it permissible for (M) to marry her or not? I hope for your guidance.

Answer: The breastfeeding mentioned is specific to the mentioned (F), if he was breastfed by (M)'s mother five times or more while he was within the two-year period. By doing so, he becomes a brother to her children, both male and female.
As for his brothers and sisters, they have no connection to the breastfeeding mentioned, and they do not become brothers to the mentioned (M). It is permissible for (M) to marry (F)'s sister, provided there is no other breastfeeding or kinship between them that would prohibit it. And success is from Allah.