J.C.
Hi, L.,
Actually, she can keep his child from him. It sucks, but it's true. My niece has a daughter, and was raising her alone, letting her go over to visit her father two or three times a week, no problem. Then one day, she calls to find out why he hasn't brought her daughter back, and he tells her he isn't going to. He's the dad, he has a right to have her, and then he filed a restraining order so she couldn't come anywhere near her. All very legal, unfortunately. She did not see her daughter again until they finally got a court date. Then she was allowed visitation! Visitation! With her own daughter that she had been raising the whole three years. How bizzare is that? And technically, they were still married! Separated, but not divorced yet.
So, while I totally sympathize with your brother, at this point he needs to wait for the lawyer to go to work. Or, IF she doesn't already have the restraining order in effect, AND there isn't a court mandated custody order, maybe he could do what my niece's ex did to her. Get her to allow him to see his child just once (be super sweet and agreeable to anything she says just to get him) then refuse to give him back and get his own restraining order against her. Not nice, but it sounds like she wants to play hardball.
Best of luck to you. Let us know what comes about.
J.