I would never de-beak birds. It is unnatural and inhumane IMO. Chickens that have been de-beaked suffer the long-term effects of chronic pain from recent studies (sorry, I can't go searching for the link tonight to back up my claims).
Can you just put the new ones in a small cage inside with the older hens...after a few days or a week they will be use to each other. Then they will have to come to a pecking order. The young ones will give the others plenty of room...of course there might be an older one that is really mean...need to watch and make sure the older ones will not over do it.
Also, how old are the young ones...are they about the same size as the older?