First Day At A New Coop
Introducing new hens can sometimes be a difficult process but the establishment of the pecking order is usually sorted out within about a couple of weeks and peace will resume again. If, for the first few days, you were able to separate the new hens from the original ones during the daytime in a makeshift run, that often helps reduce tension.
The new birds can be popped in to the coop at night when the original hens have gone to roost and as they are drowsy, very little pecking occurs during the night. If they are kept separate for a few days but within sight of each other, this really does help. If this isn't practical, make sure that you have at least two separate food sources so that the new hens aren't barred from the feeder by the dominant hen and try not to intervene if pecking does occur unless it is causing injury or distress to the newcomers who should be removed if they do seem to be suffering from bullying.
You can try to introduce them again in a few days time when things will hopefully have settled down. The sooner the new birds learn to be submissive, the sooner it is all over, especially if the younger birds are submissive from the start.