What noise does it make? At 7 weeks that is the best way to tell. If it sounds like a loud quack, it's female, if it's raspy or a quiet whisper sound, it's male.
Listen for the quack. My Olive looks exactly like my Olivia but after listening to them both Olive became an Oliver. They look alike as teenagers but will change when they get adult feathers. Found that out the hard way
Oliver has a raspy sick sound and Olivia has a LOUD quack
Just an educated guess, but I'm betting the front bird is a duck and the back bird is a drake. Bill coloration seems pretty consistent for those sexes. Don't bet the ranch on this.
They are going to look like that at 7 weeks, male plumage comes weeks and weeks later. Those saying they should have green heads, they are too young for green heads.