Ones that are laying, or getting ready to lay will have larger, redder combs. Also you can check their vents. A bird who is laying will have a larger pink vent, whereas a bird who is not laying will have a smaller yellow vent.
We'll need recent pictures to check, but as someone else already said, the ones that are laying have larger, redder combs than the ones that aren't. (this applies to wattles too, but bearded birds don't have wattles) another great way to check is looking at the stuff in that link that @aart posted.
