to me in-breeding is mother to son, father to daughter and brother to sister, too close in my opinion, i would go for uncle to niece, aunty to nephew, cousin to cousin and grandsire to grandaughter, still breeding close but far more less chance of the bad genes being exagerated.
thats the key with in-breeding. everything is exaggerated, you could get some amazing pups where all the good genes and qualities have come into the breeding, but you could get deformities on the other hand, not worth risking if very close in my opinion.
I would go with what i have mentioned above, I am all f