Hi, First off let me say that I understand what you are going theough. However, you do have options and you need to start preparing for them. I was married to an Australian and we were living here in the USA. Two years ago, my wife abducted both, my young daughter and step son and took them to Australia.
For the first few months, I didn't know that I had options that could bring my children home. My first option was to press charges against her for International Parental kidnapping. Since, I didn't want to see my children's mother in prison, I chose my other option. This involved working with the US Dept of State, Office of Children's Issues.
It was with their assistance that I was able to lodge an application with the International Hague Convention Courts seeking an Order of Return. Australia is a signatory party to the Hague and is a partner with the USA for this. By going this route, you must understand that Australia does not have enough Judges or funding to hear cases as quickly as you may wish. Further, it does not cost you anything in terms of lawyer fees. The Australian Central Authority will represent you for free.
That being said, my case took about 14 months to resolve and an additional 3 months because of my ex wife's appeal. Final orders were made and she was forced to return to the USA. We are waiting to go to Family Courts to see who gets custody. It looks very strong that I will since, she did kidnap my children and is a flight risk The sad part of this is, that Australia will place certain financial undertakings on you before they enforce their orders.
The first is, you will be responsible for paying for all of theri airline tickets. However, the National Center for Missing and Exploited Children due have funds available from the Justice Dept to cover the cost of your children but, not for your ex wife. Next, they will ask that you provide your ex wife with suitable lodging for X amount of time. This could be anything from 2-3 weeks to 2-3 months. Also, they may request that you provide financial support, as well.
If you really feel that your ex wife may abduct your daughters then, you need to starting preparing for it now. The first thing that you need to do is contact the US Dept of State and speak with the case worker who handles that part of the world. Next, contact the National Center for Missing and Exploited Children. Explore both of the earlier options and see which one you feel most comfortable with.
You should also, start getting all of the contact information for anyone that your ex wife knows in Australia with phone numbers and addresses. Start documenting anything and everthing that you can in regards to telephone conversation with your wife, children and anyone else involved. Start writing a daily journal with everything that transpires with your ex wife. Try to communicate as often as you can with your ex wife via email and save every letter that you write to her and her responses to you. Be very careful in your emails to her or she could wind up using them against you.
There are no exit controls for leaving the USA so, the moment that you suspect that she has abducted the children, act fast.
Hope this helps and good luck!