adding a new chicken to the coop

[beckysaur]

I have two Buff Orpington hens in backyard coop. They are about 5 months old. I would like to get one more chick to add to the mix. Will this be a problem? Are there certain breeds that adapt to this better?
Thanks for any advice!

 

[chookchick]

By 5 months they are going to be very antagonistic to any strange chickens. Could you possibly get two of them to introduce together? They should go through one month of quarantine and two weeks of separation by wire to get to know the others before introduction. Two can keep each other company during the process. By six months they will be almost full grown so it probably doesn't matter what age they are as long as they are the same size.