Is the wife sinful for leaving the marital home due to the husband's insults, beatings, and threats of a second wife? What is the ruling of Islamic law regarding his refusal to financially support her and their children? Is it permissible for her to work to provide for her children's expenses? What should she do about his threats of divorce, given her fear for her children?

If your leaving the marital home without your husband's permission is to دفع ضرره (ward off his harm), then it is not considered nushuz (disobedience) and your maintenance does not fall. The husband must provide for his children. You are not obligated to seek divorce, nor is your husband permitted to compel you to do so, and you are not sinful for remaining in this situation as long as the harm to you persists. It is advisable to seek reconciliation by involving wise individuals. A woman is not permitted to object to her husband marrying a second wife, and she has the right to a separate dwelling unless they both agree otherwise and there is a separate facility for each of them.