What are the chances of a man getting custody of his 3 kids if he is on disbility?

I am helping a friend to try to get custody of his children. His childrens mother does not let him see his children at all. she has cut off all contacts and has even made false police reports to keep him from seeing them because he stopped giving her money.she took him for child support but dropped it the same day because she knew he coudnt pay it. These children are in bad hands with their mother ive seen it firsthand. she leave them unnattended outside and verbally abuses them, calling them names and humiliating them. the children have told me that their mommys boyfriend hits them. this woman is also commiting some sort of fraud which ive also reported but seems nothing is being investigated. the childrens mother lives with her parents and uses a friends adderss as her residency to get food stamps and medical insurance. when these children spend time with their father i can see the love and bond between them. I have contacted the children of youth many times but its usless. The childrens mother lives with her parent but because of the children of youth involvement she kicked them out and they need to find a new home. to me this is unstable and the childrens father can provide a more stable environment and more time with the chidren. This man is in therapy from all of the hurt of not seeing his children as well as other conditions in his life. he was recently told by his doctor that he is severly depressed and was told he cannot work under his condition. he has many medical conditions and has applied for disability at the request of his doctor. he has not work for about a year and she is constantly telling him that he will not see his kids until he starts giving her money to support them. I want others opinions on this. I believe that if he cannot work and is in the process of receiving dissability he obviously cannot fulfil his responsibilities what do u think he should do?