Might be a good idea...pics of all the set up would help in giving advice.
Might be good to keep new and old part of coop separated by wire and put the chicks in the new part.
That you can free range may help, but coop is tight space for integration.
8 weeks is high time to get them outside.
Too late for this batch, but this is how I, and others, integrate chicks:
https://www.backyardchickens.com/articles/integrating-new-birds-at-4-weeks-old.72603/
Oh, and.....
Where in this world are you located?
Climate, and time of year, is almost always a factor.
Please add your general geographical location to your profile.
It's easy to do, and then it's always there!
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