advice on moving out older chicks when younger chicks still in brooder

[sayccrn]

Back story: The older chicks are about 4 weeks old and nicely, but not fully feathered. I got two more, one died (hopefully will be getting a buddy this week for her) Older chicks have been going to the chicken tractor I built if it is at least high 70's out. baby chick is besides herself if left alone, but the older chicks don't want to have anything to do with her, and just stare at her through the divider. Last night, We got a pop up T-storm and it got noticeably cooler, like low 70's, so we brought the older chicks back inside. She quited down almost immediately. I tried to put them together without the hardware cloth separating them and again the older chicks are acting scared of her. She is even trying to hop on the ones back! LOL The box is getting awful crowded already. The first batch is about a month old. I have a nice coop, I built, but it may get too hot in the sun(I have no shade). So, I don't know when I should move the older birds out to the coop. Plus, if I move the older birds out then what about them getting used to one another again? I've also heard that you are to lock them in their coop for a week. I don't think I can do that, it gets too hot here. 2 days ago it was already 87, last summer we had record breaking 90 or above for over 90 days. What's the next best step for them? Move the older chicks to the coop I built during the day or just to the tractor? (what's the best temp for them, and what's too hot in the coop, that sits in the sun, but has lots of screened windows.) this picture is from last Thursday, when I got the baby chick.

 

[esme13]

Would they be able to get in and out of the coop easily ? I’m thinking the tractor for now and adding the loner chick with the group, if they group is not much larger than the chick alone.

 

[sayccrn]

The bigger ones can get in and out to a small run under the coop. Then I made a swinging door that opens to the chicken tractor, when they can go either from the coop run or the door of the coop to the tractor. The bigger chicks have already been in the coop for a short time. they didn't want to get out, but that was when it was 87 outside, and I don't have any shade, so I was worried about leaving them in there in the heat. The baby chick has not been in the coop run yet, just the tractor, but she only wanted to climb on me. And it is too cold for her out the next couple of days. especially if the older chicks won't have anything to do with her yet. They still run from her and she chases them.