السلام عليكم ورحمة الله وبركاته أحسنَ اللهُ إليك A brother wants to marry a sister whose parents were not married at the time of her birth and still are not married. Can her father be considered her mahram? If not, who can be her mahram?

Ustadh AbdulAziz al-Haqqan
Is her father a Muslim?