The way I read this the only food is in the coop, which forces the older to go inside. The older would not need to even go inside except to lay eggs since they sleep in the run. I don't know how much time the older spend inside the coop except when they are eating or laying. Having food and water inside and outside would be my first move.
With a 100 square feet coop you have a lot more than the typically recommended room for 9 birds but integration takes more room. That 5' width may be part of the problem too if the layout inside the coop requires the older birds to pass the younger to get where they want to go. It's not just about square feet but access and the ability for the younger to avoid the older. You should be fine once they get integrated. Looking forward to your photos so I can look at access issues.
Not sure what you are doing differently this time compared to previous years, if anything. Sometimes you can just add new birds with no preparation, especially if you have lots of room, whether you do that day or night. Dad would do that with 3 week old chicks, just turn them loose next to the coop in the morning, but his free ranged. We keep them in coops and runs so they don't have that much freedom to move. That is different.
It would be good to know if it is just one or two older ones leading the attack. If they are inside the coop it can be hard to determine that. It's possible you could solve a lot of this by locking up one older one for a little while if you could get the right one. It is possible to get one that is a brute. I don't see that often at all but with living animals anything is possible.
I don't know what is going on or why, just speculation. As long as no one is being injured I'd probably keep going but there may be a few things you can do to make it easier.
