Males make a whispery waaah sound, while females will make a loud "UHT!" sound. Pick them up, and if they "UHT!" loudly, then they are a female.
The white one could be a White Layer or Pekin. Pekin will lay less eggs and be larger. White Layer will lay lots of eggs and be a "medium" size. It could also just be a white mixed breed duck.
As for breeds, there aren't many buff and fawn colored ducks. It might be a Buff Orpington duck? Or it could just be a mixed breed. I have one that was just the result of mixed breeding from multiple ducks.
My guess is the white duck could be either at this point its hard to tell; there's no tail curling indicating its a boy but its young - assuming they are predominately used as laying breeds could as well be females from tractor supply.
Listen. That's my theme music. That's how I know I'm a super hero. That, and this tiny ad told me: