First, locate a poly-friendly attorney in your area. The MNpoly site has one listed in MN, and she might be able to refer you to one in your area.
Next, contact your state Civil Liberties Union, as you might need to draw on those resources at some point.
Finally, contact some poly-knowledgeable professionals who can provide expert testimony or "friend of the court" briefs reporting that poly families are good families. The MNpoly site can probably help with that. Anita Wagner may be able to help with that, too.