[artie merlino]

Normally I would agree with all this great advice it's all correct/true/right but at this point you definetly need to get and keep your Kittens away from your Yorkies. I agree you need to re-home one of them, I vote for the Kittens to go. It's not the point of being "Aggressive" or did you reprimand them you cannot erase Years of Breeding. Even though they are your Babies and you dress and groom them they are and always will be a "Terrier" first and foremost that's what they do, whether you train them to or not. They are Hunters and they can handle the worst weather conditions w/ease. I have seen all 3 of mine run through knee high grass in the rain, fog and dark fearlessly chase anything that moves. My 2 females, Mother & Daughter will chase a flock of Ducks into the Lake and dive/swim after them if I let them!
IMO your Yorkie's are beyond the point of Training/Socializing only b/c one of them has already killed and the other has attacked twice. I'm not saying that it can't be done b/c I have Trained my 3 to do anything.......so I do have Faith in you too if it means that much to you? Otherwise save the Kittens!