I also do early integration, where chicks are brooded in view of the flock and then start coming out for face to face interaction between 10-14 days with the goal of being "finished" at around 4-5 weeks. I've done this for the last 3 batches of chicks and it's far easier for me and the flock.
https://www.backyardchickens.com/articles/short-on-time-recycle-a-prefab-brooder.73985/
https://www.backyardchickens.com/articles/short-on-time-recycle-a-prefab-brooder.73985/
Feed the whole group what the youngest ones are eating. Or in this case, since you normally use all flock, as long as its a crumble or micro pellets, the chicks should be fine on that as well. Kind of up to your preference.After the chicks are in the coop with the hens and the rooster, can the big ones eat the chick starter until the little ones are 18 weeks? I normally feed my big ones all flock with oyster shell on the side for the hens.