Adding anything new into any situation can be rough. In this case its called the "Pecking Order" and when you intro new birds they need to be "introduced" by placing wire between them, so to show them each other, let them begin to do normal things with each other through a cage or wire. After a while - good week if not more, then place them together and they will still have to be pecked into "place", but not as bad as just dropping them in. This CAN lead to death. I am not saying everytime, but you need to use care when incorperating new family memebers.
You didn't state if they are the same size- if not roughly the same size, do not place them together until they are.
Also, you didn't say the approx age of the "chicks". If they are chicks, then more then likely they will kill them.
I hope that someone else can help you out better then I, and I don't mean to sound harsh, that is not my intent. In the flock we have, they are brutal even after several weeks!