i can add my birds fine without them knowing each other but i free range on 1 acre so i put the new ones outside so there is space and they can hide and get away from the others .. if im adding new hens i keep the new hen with the rooster well the alpha rooster since i have more then one and once he accept her then it works a little better .. my main flock are 5 roosters i have more rooster but they have mates and im breeding them right now and im getting rid of 2 big ones .. and then i have 13 hens that are out with the roosters and then i have 3 more hens and 3 more roosters but they are all in different pens so they can breed .. and i have 2 hens at my house (my main flock is at my grand fathers and they have a big barn) and 7 chicks and 2 ducklings and then i have 7 more chicks coming out of the brooder soon once they are 1 week old im putting them with my chick flock and 2 hens that live outside and then 18 more chicks hatching so i will have a big flock to add with my main flock it will work out fine since the new flock coming in has size and numbers so they will have a group to be in and they will not get picked on as much since they have a big force to fight back in