I've only done this once and my vet at that time told me a formula to mix and feed the kittens w/a baby doll bottle. But a syringe will work as well but kittens like to suckle. Be sure that the formula isn't too warm or cold. And remember to gently rub their bellies w/a warm wash cloth to stimulate bowel movements. Mama is supposed to lick their bellies and this does the same thing but it sounds like Mama can't do it. But most importantly, call your vet and/or a local resuce organization. They can tell you what to do. Good luck and please keep us posted.