What is the ruling of Islamic law regarding the marriage of a foundling girl who was raised by a man and attributed to him, while she is unaware of her adoption, and a young man has proposed to her, but her guardians refuse to inform him of the truth about her lineage?

Adoption is Islamically forbidden due to the rulings it entails regarding the adopted child's lineage, such as inheritance and the rules of mahramiyyah (prohibition of marriage). The father must inform the adopted girl of her true lineage and that she is not his biological daughter, so that she does not intermingle with his sons as a stranger, unless she becomes their mahram through breastfeeding. Marrying her off as his daughter is deceit and fraud. Therefore, this must be explained to the father and brothers to rectify the wrongdoing. If the questioner is unable to do so, she should enlist some righteous people to explain to them the prohibition of adoption and its rulings that contradict Islamic law, in a manner that does not reveal that she was the one who directed them.