I'd say that epilepsy - indifferent of modern medical scientific view on medieval ability to cure/remedy it - isn't treatable by using Medicine nor Chiriurgy. Whether you define it as a result of being touched be the Devil (Infernal) or simply visions or someother Mythic power (whatever you prefer) in the terms of the paradigm a doctor would have to face resignation (even if he himself might struggle furtilely).
DC's on the others?
It's important to remember that the DC of the disease isn't on how difficult it is to cure/recover - that is covered by the normal rules on recovering from wounds. Thus the DC is only on how easy you contract it in the first place!
The Might of the spirits in question might be important if spread by them - at least if you use magic to overcome the disease, but whether this would also make it more difficult to treat with mundane mean, that's another story?
But other than that:
Leprosy: I would set the difficulty of avoiding getting leprosy as very low, since most people in the outset is immune to the bacteria. I'd aim at perhaps something as low as DC 3 to avoid contraction. But as a house rule I'd probably make the wounds next to impossible to recover from (unlike the normal wound loss from disease) and I'd impose social stigma/penalties as well beyond the physical wounds penalties.
Consumption - now know as Tuberculosis: Indeed - the term Tuberculum is from the 1st century but doesn't cover the disease as it does today (from the early 19th century). The myriad of resembling diseases was known however (some has called it the white plague) and Hippocrate actually warned doctors from even visiting the afflicted due to the danger of contracting it. Even today it's the most prolific infectious disease and 50% doesn't survive it without treatment and as most diseases it hits the harder among the poor and destitute. I'd set the DC of avoiding contraction at 6 but perhaps make the wound dependent on the infected bodypart.
Pneumonia is a term used , in more modern terms, to refer to a variety of lung infections caused by different viruses, bacteria and parasites, thus the DC and wound suffered might vary a lot - however it suits the story. Respiratory diseases are especially in the early phases very contagious - maybe DC 9? Pneumonia often follow other diseases, and general malnutrition, as the final nail in the coffin - even being called "the old folks' friend" and medieval doctor's often stated that they could only help people between the ages of 7 and 70.
The trouble with many diseases, if you can't ignore modern medicine, is that they are very dependent on the generel nutrition and living standard of those exposed to the disease - it might be reasonable to use the general living conditions modifier from the aging rolls on the chance of contracting most diseases.
There are plenty of medieval disease/medicine ressources on the net, but a really setting specific medicine source can be found in the Cause and Cure supplement (4th ed.).
Btw - if people like historic who-dunnit novels I can warmly recommend "An Instance of the Fingerpost" by Iain Pears that centers on the budding medical science and Oxford in the troubled 1660ies England
Burn her!