Both parties should file an income and expenditure form with the court. Once these are examined it should be clearer. I know you are trying to help your brother but really this is none of your business and he should deal directly with his ex partner, otherwise when too many people get involved it can lead to bad feelings between everyone which can only be a bad thing for his son. In other words it is better if your interaction with your nephew/his mother is free of any negativity revolving around money matters.