Advice please.

My broody hen is sat on a clutch of fertile eggs I have purchased. Whilst I hope to get 1 cockerel out of the hatch, I don't feel I could keep more than one. Am I right in thinking there is a 50 50 chance of half being male?

If that is the case does anyone have any advice as to what I can do with the males? At what age and how do you tell the difference?