Chicken Sexing

Okay this time i'm not just rambling, i need some advice please. Do any of you chicken people know how the hell I can sex my chickens. I keep thinking I know, then one of them looks totally different overnight! I'm estimating that they are around 16 - 17 weeks old. They are Heinz 57 variety so no feather sexing here. I am not about to squeeze their bums either, so please don't suggest vent sexing thank you!

The two that I thought were boys are the two black ones. They are slightly bigger than the others but I thought this was due to the other two being ill early on. They both also don't have such developed wattles as the others, although their combs are the same. One though, has changed his tail shape. It has become longer and less feathered. This chap is also the more dominant one of the group. I am guessing he's a cock.

This one, however looks exactly the same, wattles, comb and all, but has a much stumpier tail, like the others.

So am I just being hopeful, stupid, or is it just too early? I need to find new homes for the boys because J won't let me cook them. We may have found someone who will rehome one, but I need to know if I am giving away the right bird! I don't want to give up my layers! So any ideas gratefully received!