Here are some useful articles on integration:
https://www.backyardchickens.com/articles/integrating-new-birds-at-4-weeks-old.72603/
https://www.backyardchickens.com/articles/my-coop-brooder-and-integration.74591/
https://www.backyardchickens.com/articles/introducing-new-chickens-using-the-“see-but-don’t-touch”-method.67839/
https://www.backyardchickens.com/articles/adding-to-your-flock.47756/
https://www.backyardchickens.com/articles/integrating-new-birds-at-4-weeks-old.72603/
https://www.backyardchickens.com/articles/my-coop-brooder-and-integration.74591/
https://www.backyardchickens.com/articles/introducing-new-chickens-using-the-“see-but-don’t-touch”-method.67839/
https://www.backyardchickens.com/articles/adding-to-your-flock.47756/