I would think tht the option 2 would be OK. Chooks are not subject to Mixy. so you need not worry on that score. An adjacent run to the other chooks is a good idea and allows the old chooks to get used to the new ones.

When you are ready to put them all in together do it at night and you shouldn't have a problem, just a little mild arguement to start with but nothing serious.

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Gardening requires a lot of water - most of it in the form of perspiration. Lou Erickson, critic and poet