I have no idea what the circumstances are, but I am going to ASSUME (yeah, I know) that this isn't a situation of the dogs barking on occasion, but rather a case of relentless barking from the moment they are let out until the moment you bring them back in. Some dogs are just "barky" type dogs, while others are not...but even ones who typically aren't can get to a barking frenzy when other dogs start in.
Do you happen to know if someone may be trying to sleep during those hours you are letting them out? Someone who works a non-day shift? Or someone who has a sleeping baby? They may be more bothered by a barking dog, but it really could be ANY neighbor who just gets tired of listening to it if there isn't a real REASON for the dogs to bark.
We have a neighbor who is home with her dog all day - a Yorkie - who literally barks from the moment his paws hit the front step until she finally lets him back in. Even when he is in the house you can hear him barking at anything and everything if the windows are open. He just doesn't stop.
Our dog (yellow lab) hardly EVER barks. So when he does, I know something is up. We trained him from a puppy though, I'm not sure how old your dogs are. Any time he barked when it was inappropriate we would turn to him and give the command "Quiet" and then hold his muzzle gently. We'd have people ring the doorbell, knock on the door, walk down the cul-de-sac, etc. to show him things that he should NOT bark at.
Even when he's outside he doesn't just bark to bark. He may bark once and jump around when he sees our neighbor dog playing with his owner, but that is just because he wants to join in on the fun!
But it will likely take a lot of correction, especially if you've allowed them to just bark at everything since they've been puppies. Once one starts in, the others are likely to join. But I would try the spray bottle (even outside) if they are just in a barking frenzy with no "purpose" behind the barking, but rather just relentlessly barking.
As much of a dog lover as I am, I have to admit that the neighbor dog is not on my list of "favorites" due to his barking. It is fine for a minute or two or if he's playing. But to just sit there and bark for hours on end can grate on just about anyone's nerves when you're trying to enjoy the fresh air - inside OR out of your home.