Do you currently have a court order? Do you have any papers of any sort acknowledging that you're the paternal father? If not, you must establish paternity as soon as possible. Have your attorney petition the court for a paternity test. At the same time, inform the court that you do not wish to have your paternal rights terminated.
If you do have a court order acknowledging that you're the paternal father, there is little she can legally do to allow her new husband to adopt your children. You and your attorney should assert in court that you do not wish to have your paternal rights terminated. Ask for attorney's fees, since she is the moving party.