Fraud should be reported to wither USCIS or ICE. You can do that by writing a letter to either or both or visiting their respective websites and using the fraud reporting contact information listed there.
NYC EXPERIENCED IMMIGRATION ATTORNEYS www.myattorneyusa.com; email: email@example.com; Phone: (866) 456-8654; Fax: 212-964-0440; Cell: 212-202-0325. The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter.
If your husband was married to someone before you and if he never divorced, then your marriage is not valid, so his green card and citizenship are not valid. If he lived with you and had children with you, how do you know that his marriage to you was fraudulent? When you say you want to report the fraudulent marriage but not get your husband in trouble legally, what does that mean? Of course he will get in trouble legally if you accuse him of fraud.
Andrew M. Bramante, Rosner Partners, 216-771-5588. Free telephone consultation. You should always consult with an experienced immigration attorney to make certain that the advice you received is appropriate for your particular immigration case.
You can report this to the USCIS or to ICE.
(213) 394-4554 x0 Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.