I think this meets some of you requirements.
Bugs by aubie56
Jeff and Julie, 17-year-old highschoolers, are transported back to Earth, circa 250 MILLION BC! This was the time of giant insects and long before dinosaurs. This is the story of their struggle for survival against 10-foot scorpions and 14-foot praying mantises. These insects really existed; this is no fantasy! Join them as they cope with a real "Land of the Giant Insects."
Tags: Ma/Fa, mt/ft, Consensual, Science Fiction, Time Travel, Historical, Humor, Incest, Brother, Sister, Father, Daughter, Harem, First, Violent