I have read that breeding a brother budgie with his sister (and vice-versa) can be bad. Now I am pretty sure that in my aviary it won't happen, but what happens if it does? What are some techniques to stop it?

Just so you know I am still pretty new at breeding.....

To stop it happening dont breed in the aviary, breed in breeding cabinets / cages of an appropriate size and design

Thanks Dean_NZ.