-- I feel your pain. Try this backwards twist -- it might take a while for them to get the idea, but it'll work if you perservere.....
When the dogs aren't barking tell them GOOD QUIET! and give them a treat. It would even be better if you can keep some treats in your pocket so that they will be handy -- GOOD QUIET and a treat..... GOOD QUIET and a treat. Then when they start barking tell them QUIET. When they stop barking then you guess it -- GOOD QUIET and a BIG TREAT!!!
Good luck!