@becky7575 Both are same age? looks like one on the left is larger? if so that maybe your drake but there are other ways to tell length of head to tail legs being thick and farther apart all lean towards drake, body shaped like football with shorter tail and legs set closer under body means...
Never heard of black feet, but I have heard of black head, that's something a chicken can pass to a turkey, If your pen is large and there is plenty of space then it would probably be okay to pen chickens and ducks together for the night, problems most folks have when having a drake in with...
You should be able to tell by size then along with voice if that age. I have 3 from this years hatch 2 ducks 1 drake and there's no denying who the drake is. I haven't heard my young drake hiss yet but he does make low sounding noises where the girls do chirp. If you can get some pics uploaded...
Depends on their age too, mine start making distinct gender noises about the time the drakes start out growing the ducks. How old are the 6 your wondering about.?