Right.....
Proportion of litters born by c section by breed - bulldogs have a c section rate of 86%. If this bitch isn't from self-whelping lines then then chances are she's going to need a c section.
This is a list of all the necessary health tests for Bulldogs and this is the health scheme that the breed council run. Appropriate health screening plus knowledge of conformation is absolutely vital for breeding Bulldogs that aren't riddled with health issues. How would your BIL and SIL feel if any of the pups were crippled with bad hips or malformed spines and they hadn't bothered with hip scoring or x-raying to check for Hemivertebrae?
This is an American Kennel Club article which gives an excellent breakdown of just how much work it is to breed properly. Even in the healthiest and most robust breeds breeding well is far from just chucking the closest dog and bitch with working reproductive systems at each other and hoping for the best.
A blog post by Dr Sophia Yin concerning the issues that can arise in puppies which are hand reared. There's a very good reason why hand rearing is an absolute last resort for decent breeders. Whilst in some cases it's unfortunately necessary and it can be successful as far as the puppies surviving goes it is absolutely not the best start for them.
This whole set up sounds incredibly dodgy and they're kidding themselves thinking it's going to be a great money making scheme. How are they sorting out who pays for what? Will the breeder charge boarding fees whilst the bitch is staying with her? Who will pay for her food, vet care and anything else she needs during that period? Who is paying the stud fee? Who will pay for the c section if she needs one? Who is going to pay for all the substitute milk? What about the breeder's time investment? Raising a litter is a full time job even when the bitch is doing all the feeding, hand rearing is literally 24/7. Is this woman really going to do that for no financial reward herself, especially as she's clearly not got the best interests of either bitch or puppies at heart? What happens if the bitch only has one puppy? Or more and some are stillborn or they die whilst being hand reared? Who covers all the costs then?
There's also the potential impact on the bitch, and any puppies, both physically and mentally. A c section is very major surgery and isn't remotely risk free. They also can't expect to take their bitch away from her puppies and have no psychological fallout. Presuming the pups are immediately whisked away whilst the bitch is still in surgery, she's not going to come round from the anaesthetic and behave like she was never pregnant. Her body will also not suddenly stop acting as if she has a litter to feed. As I said above hand rearing is really not the best in start in life for puppies, either physically or mentally. Choosing in advance to hand rear a litter is actively reducing their chances of surviving and becoming happy, well rounded dogs.
Even when breeders do everything they possibly can to ensure the greatest chance of a successful pregnancy and a happy, health mother and litter things can and do go wrong. Breeding without doing everything possible to ensure the welfare of the bitch in the short term and the mental and physical health of the puppies in the long term is absolutely deplorable.
I hope they will listen to you Never and reconsider doing this.