Annika Boman, a prosecutor, told Svenska Dagbladet the girls would be charged with aggravated defamation.
"Charges will likely be formally filed at the end of April, but it may also take longer. New information may emerge in the investigation," she said.
The account set off a riot outside Plusgynmasiet high school in Gothenburg in December, The Local.se reported. Angry students gathered to try to learn who was posting pictures of young people on Instagram with details about their sexual activities.
Boman said many students have provided her with screen shots of material they say defamed them.