Around three weeks the mom will naturally start to push the pups off the nipple. Start offering small amounts of soft food (either can or moistened dry kibble). Offer food several times throughout the day, but remove anything uneaten after 30 minutes.
Personally, if you don't know who to wean pups, you shouldn't have bred your dog. Know everything before you breed. Be responsible, especially if breeding bully breeds, as there are already tons of irresponsible owners and backyard breeders breeding for money. Breed high quality dogs, not just dogs that you have. Breeding should not be taken lightly, and should not be undertaken by most who do so.
You dog is good looking. Have you competed with him in weight pull, obedience trials, show, etc? It's optimum that people breed only champion style dogs from champion pedigrees, with a hisitory of good health. This betters the breed versus only ensures cash your pocket.
Dogs are not money makers, and IMO if you don't know how to wean a litter, you probably shouldn't have bred your dogs.