I have never ever in my life heard of an adult ball python cannibalizing another. There are reports of it happening with hatchling's but it's extremely rare and the dangers of it actually happening are way overblown. It can be stressful for some animals but as long as they're eating well (they should still be fed separately) and not losing any weight, it should be fine.
I personally prefer to house mine separately, but if I'm short on space at the moment I'll frequently put like sized animals together without any qualms.