My father died sixteen years ago, and left many daughters and a son from another wife.
All the heirs have authorized me as a Wakil (legally accountable person who acts on behalf of another for a specific permissible matter) and a guardian for them through a Wakalah (appointment of a legally accountable person to act on behalf of another for a specific permissible matter) issued by the court. I brought them up and took care of them. When one of the girls reached the age of marriage, a religious and well-mannered suitor proposed to her. I concluded the marriage contract by force of the Wakalah that I have, because her full brother did not have a personal ID card at that time; as he was fifteen years old. The contract was concluded after the approval of all parties: her, her brother, and her mother, and the attendance of all the family. Now I would like to know if the marriage contract is valid or not, given that my sister bore children from her husband. Please advise. May Allah reward you best! With many thanks.
If the reality is as you mentioned, the marriage contract is valid. (Part No. 18; Page No. 154) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.