Have you punished the yorkies for attacking the cats? The cats are also part of the "pack" and should be respected... Any time the dogs show aggression towards the cats, they should not get away with it.
It's important to stay calm, but when your dogs do this they have got to be shown that you're angry with them. Your dogs will want to please you, and if you teach them that doing anything but ignoring the kitten will get them in serious trouble, they'll learn to tolerate it.
On the flip side, you could try rewarding the dogs whenever they're in proximity of the kitten, and then they will learn to associate the cat with good things. This is how I trained my cat to tolerate my pup Ollie when I brought him home. It strengthened their relationship really quickly.
Also, you could try rubbing blankets on the kitten to catch its scent and placing the blankets in the dogs' crate/around their food bowls. It's more positive reinforcement.