Kittens

My friends cat had a litter of four, and they’re about a week or two old now. The mother suffocated the runt of the litter a few days ago, so it’s down to three. My friend noticed the kittens are super week and aren’t feeding much, and he doesn’t think the mother is producing enough milk. He tries to feed them with a syringe, but it’s not going too well. What can we do to make sure the kittens are getting the milk/nutrients they need if the mother isn’t producing enough milk?

Edit: they may not be able to afford a vet visit