I don’t think the girls have to press charges. The prosecutor should be able to do that based on the evidence that they told investigators it happened and assuming the investigators have pictures.
With pictures, the girls would testify in court rather than face perjury charges.
Nope, they spoke to an investigator. Refusing to testify would not result in perjury charges. You could call them as a witness, but you really don’t want the testimony of a hostile witness.