How to stop my coop getting crowded?

I have 2 coops and a total of 12 chickens. Ten of them sleep in one coop and two sleep in the other however they are not sectioned off from one another. So how can I divide the use of the 2 houses? The older lot have started to use the other coop as a laying area but still return to the main coop at night. Im guessing the only way is to section it off and divide the flock either that or lock one of the doors in the daytime and force them into the other coop but then that may get too crowded. Ive seen other chickens on farms that seem to have lots of coops in one run so its obviously common practise. Do chickens like to have their own home and space they like to claim as their own or are they generally happy to sleep anywhere?

Thanks for any advice 

Thanks for the reply joyfull, im pleased to hear im not the only one. I guess the good way of looking at it is if I got a mite infestation then I just close up one coop and move them to the other (im sure theyd just walk round their old coop in circles looking for a way in lol). If I hatch any more chicks I shall introduce them to the less occupied coop.