We had Chinese browns too, the males will be bigger than the females, and as they get older the bulb on top will get bigger too. From the picture it looks to me like the one in the back is male. It's been awhile since this post, so you probably already have your answer, but maybe it will help...
This is my first time using an incubator and have had about a 50% hatch rate so far. I did have one chick that had a lot of trouble hatching, it was shrink wrapped I believe is what it was called. I did help a little by keeping the membrane moist, but it took about 36 hours for it to hatch...