I've read of the drama but ours was only a little in the beginning. A hatch of 2 followed by a hatch of 5, 2 weeks apart, they worked things out in the 8'x4.5' coop and small run 13'x4.5' (yes small). By the time they were 4 months, they were free ranging and all doing well, even with 2 cockerels. One cockerel culled, after I chose what I thought would be best for the flock, at 5 months old.
Spring '24, purchased 8 more for a second large coop (1 cockerel) and added 2 ISAs to the first. The ISAs were a bit picked on but the roo, now 1 yr, lightly pecked the hens who were picking on them. The 8 younger ones, would free range with the rest, little pecking but all worked out, as senior male wanted All the girls.
Maybe it was because I had many food/water stations all over, or because they free range all day every day, or maybe a good roo...I think it is all of these. With the addition of the 5 pullets (18.5 wks) and 9 pullets (14 wks), there is minimal pecking and it's usually around food...the older ones say Me First! and the younger wait and go to another food station. I have 14 food stations around the yard, close to the coops, with 33 birds. 2 have just begun to lay (Wed) and are hanging with the adults and mostly accepted.
Spring '23 Original 7: 4 Buckeyes 2 female, 2 male, 2 Marans mix, 1 SG
Spring '24 2 ISAs added
Spring '24 2nd flock of 8: 2 RIR 1 male 1 female, 2 BSL, 2 CQ, 2 BR
Spring '25 added 14 pullets (there were more but several cockerels gone) 1 BR, 1 BSL, 1 SG, 2 CQ and 9 BYM
I don't know if the breeds have anything to do with the peace.
I may separate the RIR roo next spring, to obtain eggs fertilized by the Buckeye as I would want another male like him. Keep a couple of the cockerels and watch. Hopefully they will work it out soon.