All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It is not permissible for either of you to take this money because you do not deserve any share in the inheritance of the man who adopted you. We have previously explained the prohibition of adoption and the fact that it does not entitle one to inheritance in Fatwa 119119.
In addition, life insurance is prohibited as clarified in Fatwa 81901. It is only permissible for the inheritors to take the original amount that the deceased has paid to the insurance company, so you should give this money to the lawful inheritors. If they gave you something voluntarily, then there is no harm in accepting it.
As for the extra amount, it is to be given back to the insurance company.