Seriously, it does no good to explain to you how to train the dogs. The owners must have enough interest to learn how and they must follow through. There is really absolutely nothing you can do about it, NYBoy.
It has to have taken years of very bad training and very bad management to make a Cavalier growl at its owner. It's so out of character for the breed, that they almost must have grafted a gene into their dog. It's going to take a change of the entire relationship to the dog, and if they are not interested enough to make inquiries on their own, I doubt that they are interested enough to change their entire lifestyle.
That dog thinks it is the pack alpha and everyone else is his servant. It's taken a mountain of spoiling to bring a Cavalier to that point.
If you are going to become the new owner of the dogs, and are willing to go into a massive retraining program, then ask for help.