multiple pregnant cats

Question
Hi. I recently had two mothers give birth within the same week. One mother repeatedly tried to "kidnap" the other cats kitten. We keep them separate now. Why do they do this?  Also one mom rejected two of her kittens but cares for the third.  What causes a mom to reject her kittens, and is there anything that can be done to prevent it?  Thankyou very much for your time.

Answer
Hello Frances,
First, let me start by saying can I please urge you to spay and neuter your cats? Millions are put to sleep in out country alone each year because of overpopulation. If finances are an issue please contact your local humane society or spca for resources or help.  
People love to adopt kittens and then dump them in shelters once they are a few years old. These cats are then put to sleep because people adopt the kittens and the shelters have no room, resources, space or money, so they kill the adults often. It is very tragic, and all over the world cats and dogs are gassed, euthanized or poisoned because of over-population. I know that is heartbreaking.
The less that are born means that less will be killed as there will be more adoptions in shelters etc.

Nature has a way of weeding out the weak, sometimes referred to as survival of the fittest. Something may be wrong with the kittens for a mom to reject them. Sometimes, young cats are not ready to be moms, just like a teenager might not be ready and so they reject their litter.  I do not know how old your cat is that rejected them.
I am not clear if the kidnapped kittens were the ones being rejected?
It is fine for a cat to be a surrogate mom, many communities do this for orphan kittens, as long as the surrogate mom accepts them.
Best of luck,
Shanti