That photo helps, thanks. The run isn't that bad for 9 chickens, even when they are grown. The problem is that the coop section is really small. You are in Georgia so you probably have weather that they can be outside year around. If you consider your run fully predator proof so you can leave the pop door open 24/7 you might be able to make it work. Use the coop just for a shelter to sleep and a place to lay eggs. Expect them to stay outside all day every day, regardless of weather. Feed and water outside. Not the best of situations. I'd think hard about enlarging the coop or at least boxing in a corner to give them protection against wind and rain blowing in.
By the time you are ready to start integration they will be old enough temperature will not be an issue. If you consider the run predator proof I'd put the younger chicks in there on the ground some morning when you can observe. See how they get along with the older ones. If they are OK, try putting all of them in the coop section after it is dark. If it is really dark they will probably stay up there. If you have to close the coop door to keep them in be down there before daylight to open the door so they can get out when they wake up.
If you don't consider your run predator proof I'd build a larger coop.
With that small coop section you are pushing the limits. It might or might not work.