I honestly am not sure if they should be with the general prison population. I think they should be in a mental institution. I think the parents honestly believed what they were doing is right and was the best way to save their daughter. They were not intentionally killing her. They simply had such a warped view of reality that they thought this was the best way to care for their daughter was by not seeking modern medicine. It gets even more complicated when you consider that these people do have a sense of right and wrong and have acted in the way they view as right and in accordance with the law(these people honestly believed the best way to save their daughters life was to not seek medical help). I am not even sure how you would reform them other than simply educating them on the successes of modern medicine. Of course, with the amount of "faith" these type of people have, I don't think it would work.
The other question is "how does society handle it?". The only thing I can think of is forcing people who teach that modern medicine is evil to put some sort of disclaimer on their teachings which makes it clear that this is not accepted by any licensed physicians and could put your children at serious risk.