introducing new chicks (three weeks apart in age)

[Painter_Jane]

Not sure a 'couple days' will do the trick.
How big is your run?
Lots of space makes integrations go much better.


Integration Basics:
It's all about territory and resources(space/food/water).
Existing birds will almost always attack new ones to defend their resources.
Understanding chicken behaviors is essential to integrating new birds into your flock.

Confine new birds within sight but physically segregated from older/existing birds for several weeks, so they can see and get used to each other but not physically interact.

In adjacent runs, spread scratch grains along the dividing mesh, best if mesh is just big enough for birds to stick their head thru, so they get used to eating together.

The more space, the better. Birds will peck to establish dominance, the pecked bird needs space to get away. As long as there's no copious blood drawn and/or new bird is not trapped/pinned down and beaten unmercilessly, let them work it out. Every time you interfere or remove new birds, they'll have to start the pecking order thing all over again.

Multiple feed/water stations. Dominance issues are most often carried out over sustenance, more stations lessens the frequency of that issue.

Places for the new birds to hide 'out of line of sight'(but not a dead end trap) and/or up and away from any bully birds. Roosts, pallets or boards leaned up against walls or up on concrete blocks, old chairs tables, branches, logs, stumps out in the run can really help. Lots of diversion and places to 'hide' instead of bare wide open run.
Good ideas for hiding places:
https://www.backyardchickens.com/threads/a-cluttered-run.1323792/

UPDATE: So, last night I went to check on the chickens in the coop after dark to see how the three that were left were doing while Pancit was isolated on the porch and since the other three were snuggled up together in the coop getting along great and keeping each other company, I dicided to get pancit off the porch and stick her in the coop while the other three were in there asleep. She protested and kept trying to get out of the coop like she was afraid but I eventually got her in there and she quieted down. This morning I let them out of the coop and into the run, and I also added a couple flower pots turned onto their sides and a couple of the chick feeders that they used when they were in the brooder to spread out the resources. So far so good. The big ones are not outright attacking the littles, only minor chasing going on. the little ones still run from the big guys and don't quite trust them, but everyone is figuring out their place. I think seperating the main bully really for a couple days really helped along with y'alls advice Thanks guys!