Don't quote me on this as the newer breeds can mess me up when trying to figure out sexes.
This one is a hen, a light blue cere with white nares or nostrils on budgies are hens.
The solid looking yellow one looks like a hen but I can't really see the cere close up from the front of the budgies face so its hard to tell.
The white and blue pied on the left of the pic of 2 birds looks like a cock bird.
The darker blue and white budgie on the right side of the pic of 2 birds could be a hen.
When the birds start going into breeding condition their cere's will turn a brownish tan color and look crusty. This is definitely when you know for sure you have a hen!