Is the breastfeeding sister of her husband's brother lawful for her husband and his brothers?

"What is forbidden by lineage is also forbidden by breastfeeding, but the prohibition applies specifically to the nursed child, not to their siblings. So, whoever is nursed by a woman becomes her child and her husband's child. The woman's siblings through breastfeeding become mahrams to all the children of the nursing mother and the milk-provider if they shared in the breastfeeding. However, if the mahramiyyah (prohibition of marriage) between her and your husband's brother is due to her sharing milk with him from a strange woman, or if he was nursed by her mother, then that does not make her siblings through breastfeeding mahrams to his other siblings. And merely being a sister to your husband's brother through breastfeeding does not make her a mahram to your husband and his brothers unless they shared in the breastfeeding. The breastfeeding that makes marriage unlawful is five full, satisfying breastfeeds."