Hi, I'd like to help you with your question.
It certainly sounds like your fiance's ex wife has control issues and emotional abuse issues. This makes it extremely difficult to co parent since she is not putting the children first, but her own issues first. It may be that she is angry at your fiance for the divorce and is using the children as weapons against him, or she has a personality disorder and acts this way in everything she does.
To find a counselor to work with you, you can try a few options. One, ask your fiance's lawyer for recommendations. Let the attorney know, if he/she doesn't already, that the mom is acting out in this way and see if they can recommend someone they have worked with before in custody cases that would not be scared off by the mother's behavior.
Also, you can try contacting any counselor you call for an appointment ahead of time and letting them know about the mom's behavior up front. Do this as part of your screening process so you can get the counselor's input as to whether or not they are willing to work with your family.
You may also want to talk to your fiance's children's school counselor to see what they recommend to help. Schools are usually well versed in custody issues and the counselor may be able to help your fiance's children deal with the stress of their mother's behavior.
You can also try contacting the Children and Youth services in your area to ask about counselors. Since you have already reported the mother, you may have a contact with them. Let them know you are concerned for the children's wellbeing and see if they have any ideas for you.
As far as I know, any counselor has a right to opt out of working with your fiance's ex wife. She may be threatening the counselor's with a filing a false report against them or other scaring them off with other threats. If she is as out of control as you describe, she could be saying anything to the counselor and the counselors are deciding it is not worth the risk to work with her, or that it is not productive.
You can contact the American Psychological Association for more ideas on how to approach this issue. They can tell you more about counselors in your area and who may have the experience to help you. Here is a link to help you:
I hope this has helped you,