If you have an enclosed space that will hold both flocks comfortably it can be fairly easy to integrate the two flocks.
The enclosure will need a divider
fence good
enough to keep the flocks apart but able to see each other for a couple of weeks.
Using this method means they will be able to get used to each other without the ability to peck or other wise antagonize each other.
Once they seem to be ok with each other, remove the divider
fence and let them sort their pecking order out and everything should be fine.