Welcome to duck life!
The white/yellow is likely aPekin and will turn solid white (like the Aflac duck).
The dark ones look like either Mallard or Rouen females.
The buff looks like it might be a Golden 300 hybrid.
There are a few ways to tell sex. First is if the males and females (mallard) look different. Next, and probably the earliest way to tell is by the quack they make. A female will have the traditional honk sound and be kind of loud. While a male (aka drake) has a much quieter sound and resembles a frog.
Then when full grown, the drakes will grow what's known as a drake feather. It's a distinctive tail feather that curls upward.
Hope that helps.
