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then they are still paired.
groups would be like 2 males and 22 hens.
In some species like goldeneye, that can work, well not that extreme, 2-3 extra hens is fine. But in others, mix breeding or sterile eggs will be the result is all. You wont have fighting issues unless the male ratio is super high over the hens.
In groups like you are talking about is what we all refer to as community pens, everyone does that. With the exception of just a few species like shelducks, no one keeps them 1 pair to 1 pen (like pheasants)
That's one of the major pluses to keeping waterfowl, you can build one large pen and just fill it up with what you like and usually have little to no issues with fighting or mix breeding.
Pens not cages though. To be a cage is a off the ground wire box like show chickens are kept in. If this is you thought, pass on them, they will beat themselves to death in something like that, especially wood ducks, they are the flightyest of all the waterfowl.
You need at minimum a 10x10 to me for a pair of ducks, after that, add at least an additional 50 sqfeet or so per addition pair, which for 12 pair of wood ducks would equal out to a 600 sqft pen, or a 20x 30. Bare in mind, this is bare minimum, bigger is always better. The more room they have the more comfortable they will be. A constantly stressed bird will be super flighty, pase the fence all the time, and you'll never get an egg from them.
Hope that helps a bit