I know you want to fix everything at once, but you may want to just give them a quiet few days--with clean space/bedding, food, water to drink, water to explore and bathe in--before you try to address the bumblefeet directly. As the ducks' health improves, there's some chance the bumblefoot may improve on its own. In any case, treating it is stressful (for the ducks and for you), and stress itself makes many things get worse, which is a reason to give them a few days to get used to their new environment before beginning active treatment.
I would consider NOT doing a look-no-touch introduction yet. It might be better to keep them on the other side of the property, or even further if possible, to avoid possibly spreading diseases and parasites. There's no telling what the new ducks have, but considering the conditions they came from... It's easier to treat 6 ducks than all 12, once you figure out what does need treating.
(I'm not an expert on any diseases or on ducks, just making a few guesses and throwing them out there for consideration.)