Not much of a breeder if they don't know what breed they are. From those photos I'm leaning toward a mix of different breeds. Some look single combed, some look like a pea comb. I agree to hold off a bit until you are sure. To me #4 looks male based on the wattles and the heavy legs. The others, I have no idea.
To help us try to sex them can you give us two shots of each. They don't always cooperate, some are really camera shy. A good shot of the head showing the comb and wattles. A second shot showing legs, posture, and profile. Heavy legs and an upright posture are a male thing. Sometimes body shape can say boy or girl. Experience helps but I think it is more of an art than a science. Sometimes it is easy, sometimes really hard, even when they are older.
In my opinion the easiest and most humane method is the way you can. You want it to be swift and sure. You do not want to flinch or close your eyes at the wrong time, that could lead to an injured chicken or injury to yourself. I use a hatchet and stump. I'm comfortable that I can hit the target. With the head severed I'm sure that it's not feeling pain. If you don't have a stump or are not comfortable you can hit the target with confidence, I do not recommend this method.
With practically any quick method they will have involuntary movements, the wings will flap and the legs will kick so it jumps. That can be hard for some people to watch, especially if you are nor prepared for it. I haven't tried it but using a killing cone or maybe wrapping the bird in a large towel or old sheet around the wings and legs may make that easier to watch.
There are several different basic methods such as a stump with an ax, hatchet, or meat cleaver, variations of the broomstick method, using those loppers or something similar to remove the head, some slice arteries and let them bleed to death. I've seen cervical dislocation discussed.
I have no idea which will be best for you. With that disease you are in a hard place, you are making the ethical decision but that doesn't mean it's easy.