Q: If a woman has a step son, after his father’s death, does he still remain her mahram?
A. A step son will always remain a Mahram for the step mother, even after the death of the father (Fataawa Mahmoodiyah V28 P107). If there is fear of Fitnah then the stepson and stepmother should not be alone and should not travel together without the presence of another Mahram.
And Allah Ta’aala knows best.
Mufti Siraj Desai