Answered by: Alimah Maimoonah
Assalamu Alaikum, I have been married for 18 years Alhamdulillah my wife was married before and had a daughter from her first marriage, she is 19 now and was 1 when I married my wife. It’s time for her to get married now, do I have to inform her real father of her marriage and get his permission or can I give her permission for the nikah. There has been no contact with him since separation and my stepdaughter does not even that I am not her real father my wife has not told her please advise.
In the name of Allah, the Most Gracious, the Most Merciful
According to the Hanafi Fiqh, the nikah of a sane, mature, free woman is valid without the permission of her wali. 
Although it is not advisable for a woman to marry without the consent of her wali, permission of the wali is not a condition for the validity of the marriage. Therefore, the nikah of your stepdaughter will be valid irrespective of whether or not her biological father is informed.
Only Allah Knows Best
Written by Alimah Maimoonah
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
وينعقد نكاح الحرة العاقلة البالغة برضاها وإن لم يعقد عليها ولى بكرا كانت أو ثيبا
(Hidayah, Maktaba Rahmaniyyah, page 335)