I'm not sure that having brief one-to-one "dates" is the way to integrate him, it could just be stressing him out. Plus if you separate them at the first sign of trouble you are not letting them sort it out themselves.
Have you ever been the new kid in class? It's far easier being able to sit back in a safe space and watch the way the playground works before trying to fit in.
Are you able to divide the run so that he can be out and about within sight of the others but without them being able to get to each other physically? That way he would get to see them as a flock where he can learn the group dynamic and see what the pecking order is with no pressure, in a place where each can get away to a safe place if needed. Make it at feeding time, or throw down a handful of treats so they are all more interested in the food than in the newcomer. Doing this daily would get them all used to each others presence, and also help get him used to the outside conditions. After a while they should pretty much be used to each other and then you can try having them in all the run together.
Have you ever been the new kid in class? It's far easier being able to sit back in a safe space and watch the way the playground works before trying to fit in.
Are you able to divide the run so that he can be out and about within sight of the others but without them being able to get to each other physically? That way he would get to see them as a flock where he can learn the group dynamic and see what the pecking order is with no pressure, in a place where each can get away to a safe place if needed. Make it at feeding time, or throw down a handful of treats so they are all more interested in the food than in the newcomer. Doing this daily would get them all used to each others presence, and also help get him used to the outside conditions. After a while they should pretty much be used to each other and then you can try having them in all the run together.