How do you know that? It's easy to try to justify something but not terribly realistic or fair to the animals this is directly impacting. The babies came from somewhere (i.e., adults who have managed to survive without someone keeping them safe or raccoons eating them.....) Most wild caught animals, especially those which require special care such as terrapin, don't live very long in captivity. Additionally, finding a vet willing and able to help care for them can be incredibly difficult.
If they're Eastern Box Turtles (likely considering where you're located), they're a federally protected species, require more than a 10 gallon EACH, need special lighting, someplace to soak, but not neccessarily swim....... It's illegal in most states to remove turtles from the wild and returning them to the wild after keeping them in captivity for too long can endanger them even further. I would strongly advise your sister to get them to a rehabber to rehabilitate them, ensure they are safe to return to the ecosystem (that they haven't picked up any nasties while in captivity) and return them to the wild. They will probably have to wait until Spring to be returned to the wild since they haven't had time to acclimate and prepare for hibernation.