Here is a thread on integrating chicks with an adult flock. Might be helpful.
https://www.backyardchickens.com/threads/topic-of-the-week-integrating-chicks-into-an-adult-flock.1126547/
They will most likely need to be introduced slowly. Just putting them together might not work. Especially if there is an age/size difference.
We use a "see but no touch" method. The newbies are separated by fencing (or what have you) from the originals so they can't get to each other but can...