How old are they?
Where will they be ranging?
How long have they known each other?
If you are introducing newbies to the flock it takes about 4 weeks of seeing each other through a fence to start accepting each other and then there will be pecking order contests.
If the younger of the flock have space to run and hide and get away from older established flock, they will have a better chance at adapting.
Remember...Most mother hens abandon their cicks at about 1 month anyway and the chicks have then had time to see and been seen and are usually able to run for cover!