First year flock owner here. I picked up 9 chicks and then about 2 months later I picked up 3 more. Two of them, a silkie and a polish were getting picked on in the brooder box I assume because they were smaller and new. The Amaracuana was getting picked on too but was larger and handled herself. I separated the two from the others.
At 8 weeks the older birds moved into their coop and run. During the day I’d take the other two out to the run, separate them with a dog gate and leave all the birds in the run all day. After a week I let them free range together. The Polish and silkie were bullied a little but my yard is big so they could avoid the other birds. It took about 2 months of this on a fairly consistent basis to get them to come together. Now they are one solid unit.
After doing a lot of reading on here I believe it’s due to them having a lot space in the run, space in the coop, several feeders and watering stations and getting time out to free range in the back yard. As long as they have space, food and water I think most birds will get along with each other. It eliminates things to fight over.
I have a mixed flock. Not a single one is a jerk. Some don’t like to be picked up but never an attack, good with kids and they hang out with my 80 pound Doberman.
My Polish is a goof, super sweet and gets along with all of my other birds. I think if she was raised with my other birds there wouldn’t have been any problems getting along.
Good luck!
My flock:
Rooster - Bantam Blue Sarama/Mix
Hens - Cochin x2, Barred Rock x2, Maran, Australorp, Ancona, Ameraucana, Wyandot, Silkie, Polish