When I had to introduce my new 3 to the old 3 I stuck them in the coop at night. They've had little fights here and there, but nothing the original 3 weren't already doing amongst themselves to begin with. Now, it seems the original 3 and 2 of the newer ones are beating up on the 3rd new one. She is the smallest in the group (a SS Hamburg), so maybe that's why. The others are a Barred Plymouth Rock, Golden Campine, Golden Lakenvelder, Golden Laced Wyandotte and Silver Laced Cochin.
They all generally get along, and I think that's because they have the whole yard to free range in all day. When need be, they can get as far away from each other as they wish. Maybe yours are having a war of space? Good luck to you.