What is the ruling regarding a wife staying with her husband who does not pray, and who beats her, humiliates her, and takes her money without her consent, knowing that she does not know if their marriage contract was valid?

There is no objection to the foster brother being a witness in the marriage contract. It is not permissible for someone who believed in the validity of the marriage to cast doubt on its validity after a divorce has occurred. He who deemed his sexual relations with his wife permissible before the divorce and believed in the validity of the marriage, may not deem it invalid after the divorce for a personal reason. The default is the validity of the marriage, however, a woman may request a divorce from her husband if he is unjust to her or neglects prayer.