Duckling(s) with respiratory or muscle issues?

Just heard back from the vet. She said they have congestion and she watched them doing the weird breathing. She believes it's an upper respiratory infection and wants to put them on antibiotics. Her second guess would be that they have gapeworm, but since they don't spend much time outside and haven't been on a pond or around other poultry water that this was unlikely. I hope that whatever it is hasn't spread to the others because then we're playing illness ping pong.

As far as their legs, she said they seem fine. She had them walk around a little. She was more concerned with making sure that they weren't outgrowing their bone structure than a niacin deficiency. I'll continue with the brewer's yeast and watch for improvements. They may already be doing better after getting some rest in their own tub and two days of brewer's yeast in their food. I sure hope this is the case. Thank y'all for your help and encouragement. I'm glad it doesn't appear to be anything too serious. I'll be keeping a close eye on all of them for awhile. Probably forever.

Aww! I'm glad that it is something that should heal right up with antibitoics.

UPDATE: The two Welsh Harlequins are doing better as far as the respiratory infection. They don't like a syringe down the throat when I do it, but it's almost as if they forgive me as soon as I'm done manhandling their heads.

Still have a concern for the smaller one, which we confirmed at the vet is a male (the other likely being female). On top of being smaller, he stands one foot on top of the other. When he walks he crosses one leg over the other (right leg goes way left, left goes way right), and when they run from me like I'm the devil he always ends up behind the others. I've been putting Brewer's yeast on their food consistently for over a week now, and I haven't seen much improvement. Still prefers to sit on his knees or lay down. The two of them lay down a LOT more than the others, especially now that they're separated due to the infection they had. They're in a rather small tub.

Could this be a lack of leg strength from not being able to walk around too much rather than a niacin deficiency? Or could the deficiency have been so drastic that it will take a while to fully correct itself? Even worse, could this be permanent?

Most of the pictures I see of niacin deficient ducks show them with a very wide stance

I think any of those is possible. Good nutrition, B supplements, probiotics, tub time for exercise and joy (closely and constantly supervised), TLC.

I might would try to get some Poly-Vi-Sol WITHOUT iron. It's what parents give infants to give them all of the vitamins they need. We had a chick that had trouble standing upright and it was a vitamin defeciency. You can get it at Walmart for 10 dollars. Make sure that you get the one without iron. We syringed a full syringe twice a day (once in the morning, and once at night). We also put some in the drinking water incase the sneaky little chick spat it out. It cleared up within a week.