Is the quantity of milk that the second wife expressed sufficient to breastfeed the adopted daughter, knowing that it is not enough for half a feeding, for the daughter to become محرم (unmarriageable) to the husband and his sons from the second wife?

Scholars stipulate five known sucklings for the حرمة (prohibition) to be established. What occurred does not exceed one suckling, which, according to the preponderant opinion, does not establish the حرمة. Therefore, the girl is not considered a daughter to the wife or to the questioner through suckling, nor is she a sister to their children. Adoption, in the sense of attributing the adopted child to the lineage of the adopter, is forbidden and has been nullified by Islam. Thus, it does not entail the rulings of true filiation. However, adoption in the sense of care and upbringing is permissible, and its doer is rewarded.