The answer given to the above question by Ayatollah Mahdi Hadavi Tehrani (may Allah grant him long life) is as under:
1. Being an orphanage child does not mean that the child is illegitimate by birth. In fact, if at the time of conception, the child’s mother had been married, the child belongs to that man and he/she is considered to be legitimate by birth.
2. If he knows who his mother, sister or aunt are, he is mahram to them. If they are the relatives of the woman and man who have taken care of him and he knows that he himself has no blood relationship with them, they are not considered to be mahram to him.
3. If a person has a father who is considered to be his father according to Islamic law (i.e. he had been the husband of his mother at the time of conception), he inherits from him. In case, however, he had been brought up or adopted by a man who is called his step-father, he does not inherit from him.