Based on the facts you explained it appears you should consult with an attorney about protecting your reputation and possibly file criminal charges if the the threats to you are credible. Depending on KS Law you have various rights for Internet bullying.
An action for libel or defamation requires a false statement of material fact. Nothing that you have stated in your question appears to satisfy this requirement. That does not mean that you can't take steps to protect yourself, but you need to consult a lawyer to find out the most effective way to stop this harrassment. Print out all of the Facebook statements the group has posted about you and any other information you have pertaining to their statements and take this material with you to the lawyer. Good luck.
If you have PTSD you likely will not be very effective handling this yourself. An attorney can likely get the Facebook activity stopped and taken down. Unless these individuals live in your state, suing them will likely be a very expensive exercise in aggravation.
This is not legal advice but a general comment on society based on a limited set of hypothetical circumstances. No one should act or refrain from acting based on these comments without seeking appropriately licensed legal or professional advice. The author disclaims all liability in respect to actions taken or not taken based on his comments.
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