Does your mother's boyfriend pay rent or help pay the mortgage? Does he share utillties and other household expenses?
If so, it may not be that easy to get him out unless he is breaking the law (i.e., domestic abuse), in which case your mom should get the authorities involved.
There are too many unkowns to give you specific advice.
Have you tried this resource? http://www.atlantalegalaid.org/others.htm
Good luck, Christene, to you and your mom.