In my experiences, it is best to harden chicks by not keeping them inside much longer than a few weeks. I have never had any chicks with down (baby fluff) at ten weeks of age.
I think they will be fine together since they are being free ranged. And it is another set of eyes to look out for predators and to keep the hens from ranging too far afield.
In my experience if cockerels are of similar size, the same general age and more docile types, it can work. But even then once any chink in the armor becomes evident, things can go sideways in a hurry.
The Black Stallion books by Walter Farley if you haven't read them. I loved them as a child and wouldn't mind reading them again when I retire which won't be too much longer. They took me on adventures around the world as did the others I mentioned.
I loved The Black Stallion series of books by Walter Farley as a kid in the 1960's; "The Odyssey" by Homer, "Wuthering Heights" by Emily Bronte and "The Lord of the Rings" by Tolkien were my favorite reads in college in the early 1980's. Since college I have not read as much due to work...
I got my first order of chicks from Murray McMurray in 1975 and the mail carrier actually delivered them to my home. They arrived in Lenoir, NC in two days from the hatchery in Iowa. Times sure have changed in the past 50 years.