Will Ra'ed's daughter become a sister to my husband, and is it permissible for her to uncover before him, if my husband's mother breastfed Ra'ed's daughter along with her youngest daughters?

If the husband's mother breastfeeds a female infant five known feedings within the first two years of the infant's life, then this infant becomes a sister to the husband through suckling. It is permissible for her to uncover in front of him, just like his other mahram relatives.