are you sure with such a size difference they won't get pecked to death? i had a bantie sultan that i slowly introduced to the others and she still gets picked on, and i could imagine what the hens would do to them being ten times bigger than them.
(p.s., and should i still have a heat lamp for them at this age?)
I have added chicks that age to my coop without incident. I did add branches to give them a place to hide. I think I put them up for night for a few days just so they wouldn't get picked on while the coop was closed after sunup (at 4 am.) .
I have chicks that age right now. I'm turning the heat off during the day to get them used to the folder temps. Our temperatures have been 30° F or lower and we have lots of snow. As soon as I get the light off I will be introducing them to the old coop by putting them in a wire chage for a few days. Then I will turn them out into the coop for the day but put them up at night. When they look settled I will remove the cages. If it was warmer right now they would be in the coop.
I have many more chickens so I might take a bigger risk than you would.