Clicker Training Two Dogs

Q: We have a couple of two-year-old Lab/Rhodesian/Shepherd mix "pups," two sisters that were found abandoned. We have had some success using traditional training techniques, but would like to try incorporating the clicker. Do you have any recommendations for using the training with two dogs? Even if one were indoors and the other outdoors, we suspect that both would still be able to hear the clicker. Would it confuse the "other" dog to hear the click and not be rewarded? Or, perhaps if we trained them together, would the dog not receiving the treat understand that her sister is getting a reward for the desired behavior?