I've seen young pullets fight like cockerels for their position in the pecking order. Just because you have chicks flaring out their neck feathers, staring each other down, and jumping at each other does not mean that you have cockerels. It's normal behavior for chicks between 3 to 10 weeks old, establishing the flock dynamics.
Your chicks look like they are about 5 weeks old, so it's still a bit early to be sure. Any chick that starts to turn bright red in the comb before 10 weeks old is for sure a cockerel.