I’m not a dog breeder. I can’t tell you how to select good dogs for breeding, what to look for in a healthy pup or anything like that.
What I can tell you is a couple of things.
First if you are going to breed select a breed that suits your premises. 13 Saint Bernard pups in a two bedroom apartment is a bad idea no matter how cute they are.
Second, unless you live on a farm, or intend to keep one or more to breed from, SELL THE PUPS!
It’s very easy to get attached to your new puppies, you brought them into the world an you don’t want to see them go to anyone you don’t approve of. But I can tell you one of the worst things to have in your backyard is two or more dogs from the same breed. Now I know it can work and I’ve seen examples of this, but for most people it is the start of 10 to 18 years of problems.
Dogs of the same breed, age and genetics are also closely matched for strength and determination and leadership. You can imagine with two brothers that on any one day one or the other may be top dog. This leeds to a life of the dogs constantly testing the water (that is constantly fighting each other. and if your dog lives 10 years this is bad, with some of the smaller breeds living for 18 years even more so.