Your dog has too many puppies for the number of nipples, or for some reason is unable to produce enough milk to feed them. You want the puppies to live, so you are going to need a replacement for a mother's milk. Thankfully, it is possible to replace puppy milk, and it's relatively easy. You can use a homemade puppy formula to supplement or completely replace the milk it would get from its mother.
Mix 12 ounces of evaporated milk or goat's milk and 12 ounces of baby formula. Add one egg yolk, 1 tablespoon of liquid pectin, and 1 tablespoon of honey. Mix thoroughly.
Pour the mixture into newborn human bottles with a newborn-size nipple. Nipples for other small mammals such as ferrets are not as effective for puppies, which have larger mouths.
Warm the formula to about 100 degrees. Puppies, like human babies, have trouble regulating their body temperatures at birth, so it is important to feed them formula at or near body temperature. A puppy's body temperature should be about 101 degrees.
Lessen the amount of baby formula in the mixture and replace with an equal part of water 1 ounce at a time until you find a level that helps the puppy resume normal bowel function if it becomes constipated.