This sounds serious and it could be related to a poor diet causing neurological symptoms, or some type of poisoning, or a virus affecting the muscles, nerves or the brain. I suggest you get them looked at by a vet with herp experience. He will be able to tell if this is something that can be fixed with diet or meds, or if it is ....something else. Sorry I can't be of more help, but this is definetly one of those time where the turtles need to seen by a professional.
-----
Tess Cook
www.boxturtlesite.info