Once you create a work it is automatically copyrighted. There are no forms to fill out in order to be considered legally protected.

Are these girls over 18? If they aren’t then you have even less legal recourse against them.

You could, ahem, “inform” them that if they continue you are going to expose them for the fakers (poseurs, wannabes, etc) that they are. I would think that may work, but if not you are really only left with legal action which is expensive, time consuming, and may not actually be effective if they are minors.

Sorry, wish I had better news. I recommed that you expose them for who they are, but no name calling or anything other than the truth.