السلام عليكم ورحمة الله وبركاته The mother of my wife married a few days ago with her husband. He is the step-father of my wife. But they did not marry islamicly, in church or synagoge, since theyre both non muslims, only civil Is he mahram for my wife? And is his mother mahram for me?

Ustadh AbdulAziz al-Haqqan

Yes he is a mahram for your wife, and the mother of your wife yes is a mahram even if they are disbelievers.