I kept related eastern beardies when i was younger and they never succesfully bred and the female only laid one egg that i found and i think it probably wasnt fertile. Back then i thought it would have been wrong to breed them so i didnt make any effort to try.
Im sure plenty of ppl have done it but you would be better getting unrelated ones IMO. I remember someone saying somewhere that they may not breed if they are related but im not sure how common that would be.
Pythons are differant, as far as i know its fine to inbreed them. It is a good way of knowing the snakes are the same locality too.