please do more research before breeding your dogs. have you done all the testing necessary first before you tried to breed you and your friends' dogs?
if you really want to start breeding, you need to find a experienced breeder to mentor you. and you also need to first educate yourself on all aspect of breeding yorkies. otherwise you might lose the mom and the pups if you don't know what you are doing. and you might also produce unhealthy puppies with genetic problems.
please consider spaying/neutering your dogs. that's what most responsible pet owners who care about their animals do.
there is a breeding section on this forum where you might be able to get some help from experienced breeders.