Peas have niacin but you’d have to feed a lot to give them the 10 mg they need daily so if you can get Nutritional yeast and sprinkle it over their feed 1 Tab to each cup of feed you give them.
So very sorry you lost LuLu :hugs they are all adorable.
Do the best you can and like you say they will be tiny and not weigh a lot so that is in their favor. Soft bedding can help too. Let us know how they are doing. And try not to worry ducklings are pretty tough little characters. Sometimes...
There are splints you can buy My pet chicken I believe sells them. If you can straighten the feet maybe suing the splints would keep them in the proper place only thing is you'd need to do it ASAP they grow so dog gone fast...
Have you tried placing the legs into some nice warm water just to see if the legs will relax enough you might could splint them? Just tossing out thoughts.