Ball pythons have lived for 45 years. 10-12 in captivity is extremely low.
I'm guessing a disease or nerve issue of some sort. What are the temperatures in the cage, and how are you controlling them?
Separate the two snakes immediately, you can put them in tubberware tubs, (a 32quart should be fine) and use those as enclosures.
What was the name of your breeder?