Thats strange that it seems to be all three of them's right ankle thats mainly swollen, are the left ankles even swollen on any of them? I can't tell....
Edit : Opps I see middle duck actually has the swollen left and little to none on the right it appears but its hard to tell. That doesnt look like a deficiency more like ligament/tendon damage in the ankles if its only affecting or mainly affecting one foot over another so clearly on all 3 birds. Probably their "main" feet, as I've noticed ducks have their foot they do more 'pushing' /weight baring on when running like a lot fo people do. *shrugs*
I say keep them in a small run, try a small kiddie pool with icish water (dump a piece of bag of ice in the water or a couple frozen gallon jugs of water in there 1-2 times a day) for a few days. this can help with initial swelling...so the water is cold but not freezy and actually icy, for a while. I've done this for a fractured leg before I splinted the leg, helped a bunch with swelling, then did it the next day after checking on the leg.
Also minimizing stress and them running at all for a few days, give them electrolytes for a hydration boost to the system, should also help with circulation I would think if your making sure they are good and hydrated...Niacin would be a good thing to attempt in a small dose Just in case. or first trying a vitamin suppliment to help promote healing?
If its tendon or ligament related isn't much hands on you can really do for them unless you can get splints on them that will stay on to help bare some of the strain, but I dont really think that would be necissary at all if you keep them in a small area and just restrict their activity and any excitement for a week or so.
I have no idea, I've never had sprained ankles in ducks