Question Summary:
Should I observe Hijab from my father’s two wives?

Question Detail:

My dad has two wives. Are both mahram for me

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
In principle, the stepson is a mahram (one with whom marriage is prohibited) to his stepmother[1]. Therefore, it will not be necessary for the stepmother to observe pardah from her stepson.
However, if there is fear of any fitna, especially in today’s time of immorality and in the case when the stepmother and stepson are of similar age, they should exercise precaution by not being in isolation or free talk. 
 
And Allah Ta’āla Knows Best
Fahad Abdul Wahab
Student Darul Iftaa
USA
Checked and Approved by,
Mufti Ebrahim Desai                                                                                                                                                                                                                
www.Daruliftaa.net