I'll add this one - they're very good on strategy.Yes, our courts allow anyone to bring forth a claim or initiate a lawsuit.
You should suggest to your brother that he speak a couple family law attorneys.
Divorced fathers support groups can also be helpful:
8 Fathers' and Men's Rights Organizations in the United States
Divorce Support Groups For Men: 5 Popular Divorced Dad Support Groups
California Directory of Divorce Support Groups - Divorce HQ
Divorced Dads and Support Groups – National Center for Men
Divorced Dads groups
Child Custody and Divorce Forum • Index page