The 8 month old, definitely a girl, as for the 2 month olds I can't tell by those pictures, of possible could you get full body shots of them standing up (so I can see posture) and a picture of their combs
I would say that the two younger ones are still too young to tell really. Like @Tofu the chicken said if you could get some more photos you might be able to tell but I am not sure. The 8 month old one is a hen for sure.