Is it obligatory to inform adopted children of their true lineage while their adoptive parents are still alive, and what is the ruling on adoption in Islam, and what is the ruling on bequeathing one-third of the inheritance to them?

Adopted children must be informed that they are not biological family members for several reasons: Allah Almighty commanded that a person be called by his father's name and not another's, the abolition of adoption, and because an adopted child is a stranger to the family if there is no breastfeeding [to establish a Mahram (definition) relationship]. Many rulings are tied to biological sonship, such as inheritance, loyalty, and paying blood money [aqila]. What the parents did is impermissible because Islam abolished adoption. As for the will, it is effective if it is not revoked before the testator's death.