Is a baby nursed by another mother considered a brother to the rest of the twins, or only to the twin who was nursed by her?

If twins are nursed five known feedings by another woman before they reach two years of age, the nursed twin becomes her son and a brother to her children, based on the Prophet's (peace be upon him) saying: "What is forbidden by lineage is forbidden by suckling." As for the other twin who was not nursed by this woman, they are not considered her children nor brothers to her children.