How badly injured was the chick? If the wounds are survivable, make sure they're kept clean and moist until healed. The chick, if the wounds are bloody, needs to be kept separate or it will be killed.
Chickens don't take easily to new comers. They need to have a period of separateness where they can see each other until they get acquainted. Tossing them all together when they've never seen each other before is asking for trouble. Roosters and hens are all just as territorial to strange chickens.
Now, you don't say if the new hens and new chicks know each other. If they aren't brooding hens, they have to be kept separate from the chicks. Chicks are very vulnerable, and need a safe place to run to where they can't be reached by the adult bullies. If they are hens who are mothering the chicks, they all need to be kept separate from the original flock since the new hens lack pecking order rank in order to protect their chicks from the old flock.
It's all manageable as long as you understand the limitations and take things in steps.
