Here is a useful website that talks about cults, how to help people who get involved, and support groups for families, etc.:
www.factnet.org/.
I am kind of anti-right wing religious groups, but if you want to read the other perspective you should also check out
www.religioustolerance.org. Their perspective is that unless a religious groups threatens someone's life it is not a cult and that our labeling of groups as cults is religious intolerance. I disagree, but that is a matter of politics.
Good luck, I hope that the person you care about is safe and that the whole situation resolves itself.
Laura