Hi,

My brother in laws girlfriend is cheating on him has a boyfriend. He got into a fight w/her last week and the police were called. They told him I could not kick her out because she has a daughter that lives with them.

Can he legally ask her to leave. She helps pay the bills, her name is not on the mortgage, and she does not have any signed lease.

Is it correct that he can't kick her out because she has a child?

What should his next steps be. I don't have the money to hire an attorney.

Thanks,

Yes you can evict her legally.
The police are only partially telling you what you can't do but neglecting to tell you what you can't do.
You can not evict her yourself by just telling her leave even with the police.
You have to give her a written notice (the length of days varies according to what state you live in)
Then if she still doesn't leave after that you go to the district justice/magistrate and file for a formal eviction. It will cost something like $50. To $100. But worth it I am sure.
Then they will give her a notice to leave within XX amount of days. Then if she still doesn't you get the sheriff or constables (again depending on your state) to come to officially escort her out.

Move out and rent the house to someone else, give her the eviction notice and let someone else rent out the house after that date. You move temporarily to somewhere else and lose her..