Some mothers, in all the mamal family are unable to produce milk. I think it has something to do with hormones . You should check with your vet or pet shop to see about bottle feeding. Kittens cannot tolerate cows milk but if it is diluted and has a little bit of corn syrup, it should be okay. You can use either special bottles or eye droppers. Sadly, some mothers, due to not being able to care for their young will eat them. I know this sounds awful, but it often happens to not only cats but many other animals as well. You may want to seperate them because of this. Make sure that the kittens are warm, wrapped in a blanket and with a clock to imitate the sound of a heartbeat. Take care, and take care of those kittens. Best of luck to you.