You need to quarentine the chicks from the flock for 30 days regardless before you put them all in the same coop. Then, the chicks will be old enough to integrate them. I would keep an eye on them once this is done but there will be some fighting since the baby chicks need to go through the pecking orded ahead of them. This is normal so don't be alarmed.
I kept my new chicks seperate until they were about 7 weeks old. Then introduced them slowly. If you have a seperate area where the chicks can be housed right next to the Auracanas. then they can see eachother everyday and this will be just like having them all in the same coop...It makes the transition so much easier.....trust me..