Hello

8 weeks isn't too young to be taken from mum and siblings. 7 weeks is the ideal age with regard to psychological development because it gives the pup equal amount of time to learn how to be a dog with mum and siblings and then the same amount of time to learn how to behave in a human environment and learn how to bond with people which takes place from 7-14 weeks. Taken away from mum and siblings too early, they miss out on learning how to be a dog and become too attached to people which can be a major problem and left too late, especially after 9 weeks, it misses out on learning how to be a dog in a human environment and becomes too attached to other dogs and less able to bond with people.
Pups should be weaned by 6 weeks and breeders often take mum away from them at this time although they keep the litter for a week or two longer so that isn't an issue with any pup 6 weeks or over. No pup younger than 6 weeks should be taken away from mum...ever!!!!

However, 8 weeks is too young to be out in public. In the UK, a pup can have it's first innoculation from 6 weeks but can't have it's second until 10 weeks and has to wait another week before it's safe to go out so 11 weeks is the earliest age a pups should be out in public if it has had it's proper jabs. If not, it risks picking up a number of possibly fatal infections.

Breeding a brother and sister is definitely risky in my books. They are too closely related. I have heard of an accidental litter of staffies who's parents were siblings and nearly all the pups died very early on. I'm not sure what happened to the remaining. This type of breeding definitely shrinks gene pools and contributes to genetic disorders in my opinion.