Sounds like your doing great so far and should be close to letting them all mingle together/integrate. You may have an issue with your roo/hen ratio having the 2 boys if they decide to want to fight over the girls eventually, and may have to come to a decision to only keep one, if they can't get...
It seems to me they're just not used to eating the 'treats' that your giving them. I think they'll come around by watching what the others are pecking at. All sounds normal with newly acquired birds getting used to new surroundings and new foods.
I just caught your edit and apparently was just paying attention to your feed question and missed the ages.
I have 12 weeks olds on chick starter still in their coop that's attach to the bigger coop, but I don't worry about them eating the all-flock when out free ranging.
Sorry I missed that.
How long have you had them? And what 'exactly' are you feeding them?
My thoughts are they are chickens and genetically know how to be a chicken, so they will dust bathe etc. when they need to. As far as your other older hens? The newbies will stay far away from them for now, til they get used...
I'm right there along side ya, I'm trying to get into breeding and selling. The wife says I'm "breeding and keeping"
Back to rule #1... I'm not arguing with her. 🤣