My boyfriend has a daughter that he has been taking care of since she was born, he and her daughter's mom had decide to take care of her 2weeks, he has her every 2 weeks and she has her every 2 weeks, he made the mistake of letting her apply for help through DSHS, she gets help from the state, she gets money, medical, food stamps etc.. Since she started getting money through the state they automatically put him on child support and he has to pay back the money she has been getting from the state, I know when she applied for TANF she never told them her daughter stays with her dad every 2 weeks in a month, she is probably getting that money for herself, is there any way we can get sole custody of her because her mom did that? He also doesn't have a parenting plan with her because he thought he trusted her.. what steps should he take? HELP

If she did not disclose the living arrangement of the child when applying for state aide, she is committing fraud.

Without a legal custody decision by a court, your boyfriends rights could be in jeopardy if the state gets involved in some type of investigation.

I would attempt to get a legal custody decision in place, and then turn her in for fraud.

You can and should inform the government agency about it, But there should be a legal custody agreement in place, what does it say, if she wants full custody he will have to go to court for that.
And child support should be court ordered, by who has the child and when, that needs to be taken to court also