I'm no duck expert, but to me, they look like females. Do they still chirp/trill sometimes, or do they hiss/huff?
I have Muscovys as well, and my drake isn't quite a year old yet, but he has a ton more of the red stuff around his face, while my hen has very little like these two ducks. My hen is also much smaller than my drake, so if the birds are on the smaller side, they're probably female.
Like I said, I'm a newer duck owner, but I hope I helped in anyway.