If you think it's bullying, then standard advice is do not remove the victim, remove the bully. If you take the bully out of the equation for a cpl of days, it restructures the hierarchy & the bully gets taken down the totem pole, so to speak.
I had a group who, while still young(5-8 mo? I'd have to dig back further than my short term memory is digging today) who picked on EVERYONE, even the adults. There were 3 males and 2 females in the group. I watched until I figured out that the 2 females were just groupies that ran with them but cause no harm, so they also went in the coop.(they're still groupies).
That left the 3 young male troublemakers, and 2 adult jumbo males. For 2 weeks, the hens all slept safe and comfy locked in the coop & got to free range undisturbed. My coop is divided by a pop door so the front can be closed up or left open to the run. So for those 2 weeks, none of those 3 slept in the same place or with the same bird 2 nights in a row. They didn't get to free range with the hens or all together, they got to go out for awhile on their own with the jumbos. For all of their attitude, they didn't like sleeping out in the run in the dark by themselves, and the jumbos weren't cuddlers.
It took the full 2 weeks for 2 of them. Zuri caught on quickly & got to go in the coop early. But after that, there was no further bullying. When I added 14 keets this year, I had a cpl of hens who needed time to warm up, but no trouble out of the previous bullies.