Here are some noted differences between them if it might help any of you with your guesses:
The ducks-one has a more upright carriage, raspier peep and is more social
The other has a bigger “chest” area, walks more horizontally and has a clearer peeping sound. It is also a bit more nervous acting.
The chicks-one is significantly bigger (supposed to be same hatch/type), less fuzz, more real feathers, bigger/thicker feet and legs, definitely more tail.
The other smaller and “rounder,” more fluff.
I don’t see a big difference in combs/waddles....