The only issue with this is that the cats will almost invariably learn that the cue for the unpleasant sensation of water is you + spray bottle...therefore MOST cats will continue to scratch provided you + the spray bottle are not in the vicinity. Of course the same goes for my hissing suggestion though it may be more effective due to the "social disapproval" shown (assuming they take it that way...I'm better versed in dog behaviour than cat admittedly).Get a spray bottle and fill it with water.... when the kitty scratches furniture, don't say a word, spray the furball in water.
It doesn't take long for the message to get across... but make sure that there's a "proper" place for the kitties to call their own to scratch at.