Answered by Shaykh Yusuf Weltch
Question
Is my wife a mahram in the eyes of my stepfather? Is she supposed to cover herself in front of him and not touch him?
Answer
In the Name of Allah, the Most Merciful and Compassionate
A woman is not considered un-marriageable kin (mahram) to her husband’s stepfather. Due to this reason, she must avoid physical contact, seclusion, and exposing any part that is impermissible for a non-mahram person to see. [Ibn ‘Abidin, Radd al-Muhtar]
Hope this helps
Allah knows best
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani