As salaam Wa alaikum,
Are my stepfather sons from the ex-wife, considered mahram for the daughter whom he had with my mother?
Wa Alaikum As Salaam,
Yes, the sons of your stepfather from his ex-wife will be mahram for the daughter whom he had with your mother. They all share the same father, and the sons will be half-brothers of the girl.
And Allah Knows best
Mufti Waseem Khan