He married a Christian girl in the presence of
    her kaafir brother
Question

                I made zeena with a christian girl and she
      became pregnant.In my ignorance,I thought I would make the situation right and marry
      her.We were married in the masjid with the imam,another muslim brother,her brother and her
      mother as witness.She was not muslim at the time of our marriage.She did later take
      shahadah before our child was born.What is the status of our marriage?What is the status
      of this child?What is the status of my other children by her?I have regret and remorse of
      what I did and I do not want go back to this,but I am concerned that my marriage is not
      even legal,in which case I would find myself in the same sin.What do I do to relieve
      myself of the predicament I have gotten myself into?
Praise be to Allah.This marriage is considered to be null and void, because
    it happened when she was pregnant as a result of zinaa, and because it was lacking in one
    of the essential conditions of marriage, which is the presence of two male witnesses and
    the acceptance of her guardian. On this basis, the marriage contract must be repeated with
    a Muslim walee (guardian) or qaadi (judge). The children should be named after the father
    on whose bed they were born and the father should not disown any one of them, because
    “the child is for the bed.”
And Allaah knows best.