Victoria Stillwell covered this topic on "It's Me or the Dog." She instructed the owner to put a rug near the door as a designated area for the dog to sit when the door is opened for visitors. Then she trained the dogs to sit on the rug when the bell is rung and wait quietly for the visitors to enter. This requires the dog to know the sit and stay commands well. Victoria used treats and repetition.
If you have a patient friend willing to help, have them ring your doorbell. Don't open the door until the dogs are sitting quietly in the designated area. If they break their silence, close the door and start over. With Yorkies, I imagine this would take a lot repetition and patience.
