Its hard to tell in the pictures, but I think you have 3 hens and 1 drake.
You can't always go by bill color because I've found that not all females have dark bills so they can easily be mistaken for a male. But by looking at yours, you have 3 dark bills (females) and 1 light bill (male).
I can see why you would think all drakes, because of the pattern on their heads. But a lot of the females (hatchery ones) have a dark head to start off with. If you look closely, around their eyes and the very top of their head, if drakes, the feathers will start turning green and their whole head will eventually be fully green. The females won't get green heads.
Also, if drakes, they will get a curly "sex" feather at the base of their tail. Your look like they are still too young for the sex feather, but that should show up around 3 1/2-4 months old.
Also, they look big enough for voice sexing. If you pick them up, the females will have a very loud, almost ear piercing quack. The males will either make no sound at all, or they will have a quieter, more raspy sounding quack.
I think i ended up with 4 drakes?![]()