What is the ruling on breastfeeding a baby girl by her paternal aunt, and when is a full رضعة (suckling) counted, and what is the ruling on her marriage to the sons of her paternal aunt?

It is permissible for a baby girl to be nursed by her paternal aunt. The default is permissibility unless there is evidence to prevent it. Breastfeeding is considered valid if the infant latches onto the breast and nurses five times until he voluntarily stops feeding. At that point, the girl becomes mahram to her paternal aunt's sons, as they become her brothers through suckling.