Sometimes integration goes so smooth you wonder what all the worry was about and sometimes chickens wind up dead. From what I can tell from your posts, yours is not going all that badly, even if it is not real smooth. I think you will wind up successful.
Some flocks have a chicken in it that will seek out and destroy other chickens, whether younger or a just-not-yet-integrated chickens. Usually this is a hen, but it can be a rooster. Most flocks don't have these, but they do exist in some flocks. Often a rooster makes integration go smoother because he keeps peace in his flock, but sometimes the rooster is the problem. Each chicken has its own personality and each flock has its own dynamics.
What you can expect is that the younger chickens will try to stay as far from the older chickens as they can. When they are out free ranging, they will not mix. It really helps to have different feeding and watering stations so they can stay apart. The older ones are higher in the pecking order and will enforce those pecking order rights if the young ones violate their personal space.
I find the roosts are the worst place for mine during integration. When they are in the coop together, don't be surprised to see the young ones go to roost very late. The older hens, and usually the older ones lower in the pecking order, can be especially vicious on the roosts, so the young ones try to avoid them. I've actually had young ones that were roosting on the roosts move to other places for roosting to get away from those vicious hens, including starting to sleep out of the coop. In the morning, the young ones will stay up on the roosts out of the way while the older ones are on the foor.
During the first week or so of them sleeping toigether, I make it a point to open the pop door as early in the day as I can to give them some separation.
I usually let them sleep in separate places the first week or so after they start free ranging together. Sounds like your tractor may suit those purposes. But eventuallly they are able to stay in the coop together without any getting hurt or seriously picked on.
I find that mine normally stay in separate flocks until well after the new ones start to lay. Eventually they do start to hang out with the older chickens, kind of making friends in the other flock, but this takes a long time. I raise them for meat as much as eggs, and I find this mixing occurs when I have messed up the pecking order in the established flock.
Don't expect yours to play nice together for a long time. It just does not work that way. But with the space I think you have, I think you have an excellent chance to get them to co-exist without hurting each other, which in my book is success.
Some flocks have a chicken in it that will seek out and destroy other chickens, whether younger or a just-not-yet-integrated chickens. Usually this is a hen, but it can be a rooster. Most flocks don't have these, but they do exist in some flocks. Often a rooster makes integration go smoother because he keeps peace in his flock, but sometimes the rooster is the problem. Each chicken has its own personality and each flock has its own dynamics.
What you can expect is that the younger chickens will try to stay as far from the older chickens as they can. When they are out free ranging, they will not mix. It really helps to have different feeding and watering stations so they can stay apart. The older ones are higher in the pecking order and will enforce those pecking order rights if the young ones violate their personal space.
I find the roosts are the worst place for mine during integration. When they are in the coop together, don't be surprised to see the young ones go to roost very late. The older hens, and usually the older ones lower in the pecking order, can be especially vicious on the roosts, so the young ones try to avoid them. I've actually had young ones that were roosting on the roosts move to other places for roosting to get away from those vicious hens, including starting to sleep out of the coop. In the morning, the young ones will stay up on the roosts out of the way while the older ones are on the foor.
During the first week or so of them sleeping toigether, I make it a point to open the pop door as early in the day as I can to give them some separation.
I usually let them sleep in separate places the first week or so after they start free ranging together. Sounds like your tractor may suit those purposes. But eventuallly they are able to stay in the coop together without any getting hurt or seriously picked on.
I find that mine normally stay in separate flocks until well after the new ones start to lay. Eventually they do start to hang out with the older chickens, kind of making friends in the other flock, but this takes a long time. I raise them for meat as much as eggs, and I find this mixing occurs when I have messed up the pecking order in the established flock.
Don't expect yours to play nice together for a long time. It just does not work that way. But with the space I think you have, I think you have an excellent chance to get them to co-exist without hurting each other, which in my book is success.
My first instinct was to build a mini coop for the newcomers and I read your comment above. Sounds like this is a safe option. 
