Yes, one dog at a time to break the barking. They're not to toy with the ducks AT ALL, avoid any and all excitement when they see the ducks. Work with one dog after another, daily, for a couple of weeks. On leash. Walk them up to the ducks, getting after them for every little bark in the direction of the ducks. Once they grasp the concept, work with them as a group so that pack mentality doesn't set in and undo the training.
If they stare at the ducks for more than 3 seconds, bump the leash and divert their attention. Too much focus through a simple stare will escalate to a bark, break the staring, break the barking.
When doing the group, stand on the fence line to the duck run. When they approach, shoo them back. Let them know you mean it, the ducks aren't toys or novelty critters they can bark at.
Likely they charge as a pack full speed ahead and start the barking before they're even at the ducks? On leash, they're just not allowed to do that. They can approach calmly, or they don't go at all. Don't let them "drag" on the leash in an attempt to get to the ducks. It will eventually transfer to off leash and as a pack behaving but it's a long haul to get there.
You have to work with them daily, and they're not allowed to be exposed to the ducks without supervision. Very little thing about those ducks needs to be corrected. They already had "fun" with one, so you need to be real serious about correcting it or just leave them away from the ducks and have plenty of secure fencing. The training... 3 dogs, 15-20 minutes a day, one at a time, over the span of several weeks with group lessons thrown in too. It will be a time commitment. One may grasp it faster than the others. See if you can spot the one who starts it and does it worse than the rest, and put more focus on that dog.
If they get to the ducks without supervision or discipline, it will undo the training. So be very vigilant and treat every duck encounter as a training session. Take a dog with you on the leash when you go to fill water containers or feed, and rotate which dog it is. The rest stay put up, you can't correct all of them effectively until they each know what you're getting at.
No staring, no charging, no barking, no excitement. Ducks are off limits, period. Maybe later they can have a mild interest if they behave, but through training, nothing. Give them an inch, they'll take a mile.
At our old house, we had two lunatic dobermans next door that would run their fence and bark their heads off at my dogs, and the 10+ deer that would walk and graze behind our fences. I wasn't going to let my dogs do that. On the leash they went. Once they understood what I was getting at, I stood on the fence line and kept them back. Logan proceeded quickly through the training and was allowed to sit and stare at the deer because that's all he did. My lunatic dog, learned she's just better off to totally ignore everything. She's incapable of watching with out building up excitement.
When my dogs started to ignore the Dobermans next door, the dobermans chilled out too. They realized the fun was over and they shut the heck up too. Still went off on the deer, which let me know to get out and resume training to keep my dogs solid on the "No barking and running the fence at the deer" rule. I had to drag my butt up off the couch during my favorite shows to make corrections until they were solid on it. No waiting for commercial break or all my work would end up for nothing.
Once you start it, you have to stay on it. The end result is well worth it though. When we moved here, the dogs easily accepted the birds. They didn't even think about charging the run fence, charging fences is a no-no, I don't care what is on the other side. The neighbor kid teases them through the fence from his side, or tries to anyways. I don't know why he can't listen when we and his mom tell him it's not a good idea to tease 2, 100 pound German Shepherds. But they ignore him, as if he were only a deer. They barked at him once, and I was like... No, remember? Doesn't matter what's outside the fence, it's your job to protect what's inside.
Deer, idiot dobermans, chickens, ducks, neighbor kid.... all of it gets ignored and treated with respect. It took about 3 weeks to get it through their skulls I wasn't kidding about the new rule. And it's ongoing keeping the rule in effect. I check out every bark I hear to be sure they aren't breaking any rules. I don't have to monitor them outside anymore, and I can tell by their bark what the issue is. They call right off it, immediately though. They stop in their tracks and return to me. Bonus of the training, the good behavior carries over to other things.
Your tough part will be conquering the pack mentality between the 3 of them. That's why you teach it to the individuals, and then work with them as a group.