Is it permissible for me, according to Islamic law, to inherit the house from my adoptive father, knowing that adoption is forbidden? What should I do in this difficult situation? Is my marriage valid? What is the ruling of Islamic law regarding adoptive parents? Is there expiation if they made a mistake? What about using their non-original family surname in all my official documents?

Adoption, in the sense mentioned, is not permissible in Islamic law, and the legal rulings pertaining to children do not apply to it. You are not entitled to inherit the aforementioned house or any of the man's properties, and you must hand them over to his heirs. If the man made a bequest, it would be limited to one-third of his estate. Your marriage is valid, but you must be attributed to your biological father. If you are able to change the documents to reflect your biological father, it is obligatory; if you cannot, there is no blame upon you for using them. The family that adopted you did well in sponsoring you but erred in adopting you. They must repent, seek forgiveness, and increase their good deeds.