What is the explanation of the Hadith: "What is prohibited by fosterage is what is prohibited by lineage," and does it include marrying the sister of a foster brother if they were both suckled by the same woman?

Your foster-sister (from breastfeeding) is not forbidden to you as long as you did not share in theact of breastfeeding with her. A woman becomes forbidden to the infant (she breastfed), and it is permissible for the infant to look at her, be alone with her, and travel with her. As for the man whose milk it is, the sanctity of breastfeeding is established between him and the infant, so the infant becomes his child, and the man's children become the infant's brothers and sisters.