You didn't fail at all. From what I read of your post you didn't just buy em and throw em in a tank like some do. You care to make their living quarters most comfortable to them. I would say you just ran into some extremely bad luck cause the snakes already had something before you purchased them.
On keeping them in the same enclosure, I also keep my two normals in the same tank. They were bought as a pair and I have not seperated them. I don't really see the need to right now. The albino and hets I got do stay in seperate tubs though
Just clean and pick ya up another FROM A DIFFERENT PLACE. Good luck!!!!!