I think it's probably Andrea or Liliana herself who turns back time. At the very least, Andrea too must've gone back in time. Why else would he put a restriction on François?
As for Liliana, I think her regression is different from Marius and François. It doesn't affect her mentally as much, probably because she or Andrea put some kind of seal on her mind. And that seal is probably what causes her terrible fever. (Also, unrelated, but kids getting fever so high and so long is so scary. They can literally die from it.)
But hey, it's all just speculations. If there's a novel, I never read it.
I think it's probably Andrea or Liliana herself who turns back time. At the very least, Andrea too must've gone back in time. Why else would he put a restriction on François?
As for Liliana, I think her regression is different from Marius and François. It doesn't affect her mentally as much, probably because she or Andrea put some kind of seal on her mind. And that seal is probably what causes her terrible fever. (Also, unrelated, but kids getting fever so high and so long is so scary. They can literally die from it.)
But hey, it's all just speculations. If there's a novel, I never read it.