I am so glad you like my website. In answer to your question about your dogs shaking:
First of all good for you that you have thoroughly checked out any medical reason why they shiver. That was definitely a good first step.
It sounds to me that your two dogs are simply shy. It would actually cause me to hesitate continuing to breed them, especially together, as they will tend to perpetuate this negative trait in any offspring they have.
However all is not lost. I have occasionally had a shy dog, and I found that it is basically an issue of confidence. A fabulous way to instill general confidence in your dog is obedience training. There are lots of good classes available, from store classes to professional trainer group classes to training clubs affiliated with the AKC. Just be sure to do the training yourself. It does you no good to have your dog confident around his or her trainer, and you will have a lot to learn as well.
Additionally please make sure when you work with your dogs that you don't feed their anxieties. A solicitous voice, bending over them to reassure them communicates to your pet that you are worried that they are okay. They will respond to this by being more worried! Not what you are going for! No, your attitude needs to be: of course they are wonderful, of course they can do this -- you need to be calm and certain. This will give them every chance to be so as well.