1) deed of adoption ought to have been executed by your mother by in favour of step father
2) child should not be more than 15 years unless there is custom in your community which permits such adoption
3) section 10 of Hindu adoption act
0. Persons who may adopted.-
No person shall be capable of being taken in adoption unless the following conditions are fulfilled, namely :-
(i) he or she is Hindu,
(ii) he or she not already been adopted.
(iii) he or she has not been married, unless there is a custom or usage applicable to the parties which permits persons who are married being taken in adoption.
(iv) he or she has not completed the age of fifteen years, unless there is a custom or usage applicable to the parties which permits persons who have completed the age of fifteen years being take in adoption.
4) your step father name cannot be reflected as your father in passport