2-3 is way better than one. Do it when you can be home. Another trick is to let the original birds out into the yard, and lock them out of the coop/run set up with the newbies inside the set up. This allows the newbies to explore and figure out the set up at their own pace, without being chased for their lives. Just before dark, let the old girls back in just before dark, the urge to roost will be mostly stronger than the urge to fight, kind of sort of.
The new birds, after being in there most of the day, will naturally go into the coop, and sometime they will wake up together and be fine. If not, if they could spend the day roaming the yard, this time with the coop/run open to everyone, you just might be fine.
There is a chance this won't work at all, and a lot does depend on available space, the smaller the space, the worst it will go. Adding platforms and roosts in the run, along with hide outs, allows birds to use more of the vertical space which with hideouts can really help.
Wishing they will all just be nice won't work at all.
Mrs K
Actually, 280 square feet, should really help. This is going to sound crazy, but I have also gone in and "rearranged the furniture" when adding new birds. Kind of confusing to all. Seemed to help. They are basically the same size and same age, this might go pretty good.