Is it permissible for me to marry a girl if my brother's wife breastfed her once or twice?

The preponderant opinion is that the nursing that establishes prohibitive kinship (mahramiyyah) consists of five or more satisfying breastfeeds. The testimony of a single woman regarding breastfeeding does not establish prohibitive kinship according to the majority of scholars, except if she is trustworthy, according to the Hanbalis. If it is proven that the girl was breastfed by your brother's wife with breastfeeding that establishes prohibitive kinship, then she becomes unlawful for you only if the milk was from your brother. Therefore, it is permissible for you to marry that girl unless prohibitive kinship is established from another direction.