You will likely get better results if you keep this in family court, laying out all the facts before the court regarding how this woman has endangered your children, and then asking the court for the appropriate orders.
This is NOT legal advice, is GENERAL INFORMATION ONLY, and does NOT establish an Attorney/Client Relationship with you. Therefore my answer cannot address your specific legal situation and you should not rely upon my answer in your legal matter. I am an attorney licensed in Maryland and California.
Regarding the photos, if these photos were taken in a public place or space visible from the public areas, there is no legal expectation of privacy in them and anyone can post them without the parents' permission. Also, when you post photos online, you lose any claim of privacy over them. So your husband's own actions in posting them did that. Regarding the rest of your post, deal with it in the context of the family courts. Opinions, slurs, name calling and insults are protected free speech, and for defamation, it has to be a false statement of act, and you have to prove to the court you suffered economic damages as a result (I don't see how you can do that, and legal fees don't count). A lawyer will want at least $5000 retainer plus their hourly fee. Also, since truth is a defense, the defendant is allowed to conduct discovery on every aspect of your life, depose people you know, get documents on you--and you can't claim privacy. You'd be letting her invade your whole life.
We do not have an attorney-client relationship. I am not your lawyer. The statements I have made do not constitute legal advice. Any statements I have made are based upon the very limited facts you have presented, and under the premise that you will consult with a local attorney. This is not an attempt to solicit business. This disclaimer is in addition to any disclaimers that this website has made. I am only licensed in California.
If she doesn't have the right to use the specific pictures, send a take down notice to Facebook. https://www.facebook.com/legal/copyright.php?howto_report
If she has pictures she has the right to use, meaning she took them and owns the copyright or something along those lines there isn't too much you can do.
Address the matter in family court.
Defamation would be difficult and expensive. Speaking about your husband's sex organs in a derogatory manner isn't really something that anything can be done about.
I am licensed in Pennsylvania. Members of my firm are licensed in various states, including Pennsylvania, New Jersey and New York. We handle cases involving personal injury (car accidents slip and falls, etc.,) medical malpractice, nursing home abuse, workers' compensation and social security disability. This post is not legal advice, but instead contains general educational information. Please do not act or refrain from acting based upon what you read in this post. Also please remember that this post does not form an attorney/client relationship between you and me. If you have specific legal questions, you should contact an attorney in your state for assistance.