The laws regarding child support and back pay can vary depending on your location, as well as the specific circumstances of your case. Therefore, it's crucial to consult with a legal professional who is familiar with the laws in your area to get accurate and personalized advice.
Typically, child support is intended to provide financial assistance to the parent who has primary custody of the child. As you and your brother are both adults and no longer living with your mother, it's unlikely that you would be eligible to receive child support payments directly.
However, the situation may differ regarding the back pay and monthly stipend your mother is receiving. If the back pay is owed for a period when you and your brother were minors and living with her, it might be considered legitimate. The monthly stipend may also be related to other forms of assistance unrelated to child support.
To understand the specific nature of these payments and whether there's any possibility of receiving financial support directly, you should consult with a family law attorney. They will be able to assess the details of your case and provide guidance on any potential legal options.
Remember that laws and regulations can be complex, and professional legal advice is essential to navigate such matters properly.