Introducing pullets to the flock

Hi!
We have three 8 week old pullets still living in their brooder. We have a flock of hens a little over one year old. Pullets are fully feathered, but we are hesitant to put them in the coop/run because so far during supervised free range time the hens are brutal to the pullets. We don’t have a way to separate them except for keeping the pullets in their brooder which they are quickly outgrowing.

Also, once we get the pullets in the coop, how do we keep the babies on medicated chick feed and the hens on layer feed?