There is also an excellent possibility that you simply got imported snakes that had parasites or bacteria that took 120 days to kill the first snake.

That is not an uncommon scenario. Babies go through all kinds of crap.

If I think the people you got them from are who I recall them as being, then substandard snakes would be no surprise at all.

Did you get fecals done or use any meds at all on the babies when you got them?