Is it permissible for an adopted young man and woman to take the entire inheritance of the deceased adoptive father, even though there are legal heirs, knowing that the adoptive mother urged it and all parties are in agreement?

Adoption, in the sense that the adopted child becomes like a biological son in terms of treatment, marriageability (mahramiyya), inheritance, and carrying the adopter's name, is forbidden by Islamic law and was abolished by Islam. However, if the intention of adoption is sponsorship and upbringing, while the sponsored individual retains their true lineage, then it is permissible and considered an act of righteousness.

Based on this, the two adopted young men do not inherit by Islamic law from their sponsor, due to the absence of the legal causes of inheritance (lineage, marriage, wala'). The family can bequeath to them up to one-third of the estate or less; anything exceeding one-third reverts to the legal heirs. It is permissible for the heirs to relinquish their share to them with their consent and good will, provided they are adult and of sound mind.