I hope everything goes okay for you. One thing I would mention is that adding chickens to your flock should be a long process - keeping them separated for at least a month to be sure they aren't introducing new health problems.
https://www.backyardchickens.com/articles/adding-to-your-flock.47756/
https://www.backyardchickens.com/articles/adding-to-your-flock.47756/