To answer the original question, it doesn't matter if you breed ANY species siblings. Some species tend to have on average more negative traits than others, human being the most famous. On average humans have a lot of screwed up genes, so it's not the greatest idea to be hooking up with family statistically. However ball pythons do not appear to have too many negative traits on average, so it is generally accepted as fine.
You seem to have misunderstanding of genetics and also the frequency of mutation. I would spend way too much time commenting on all of those, so all I will say is:
Please read this:
http://ball-pythons.net/forums/showt...Basic-Genetics
and do research on this:
http://en.wikipedia.org/wiki/Mutation_rate