Hello there!
I'm sorry to hear that your chickens won't except the 3 newcomers
Do they access to food and water? This is definitely a must. Make sure you have plenty of feeders and waterers.
As
@Lady of McCamley said, integration won't happen overnight.
The most important peace-making technique is to allow the birds to see one another, and even be in the same SPACE together, without having physical access to one another. This will allow them to work out the pecking order through subtler cues. If you have a run, you can achieve this by putting the new birds in the run with your old-timers but separating them with chicken wire, hardware cloth, or something else that'll do the same job. (Making sure, of course, that they all have access to food and water.) Do this for a week, or even two, before letting them in with the main flock.
After that first week, when you're ready to make the transition, some people advise that it's easiest to first introduce the new birds once they're all sleeping--the idea being that upon awakening your resident flock will notice the new guys but be too groggy to realize that things have changed, and/or too interested in eating to attack them right away. This doesn't seem to always be the case--some girls do notice immediately!--but morning introductions can't really hurt.
A few warfare-alleviating tactics we can say with certainty that reduce fighting all involve distraction. If your girls have nothing better to do they'll chase the poor newcomers and pick on them relentlessly. Distract them and you'll find they're much less mean.
- Hanging a treat such as a half a head of cabbage just out of reach so the chickens have to jump to get at it, an odd but miraculous solution;
- Adding large branches to the run and even inside the coop if possible, making pursuit more difficult and giving the newcomer(s) a place to hide;
- Adding dead leaves, grass clippings, pulled weeds and/or table scraps to their run, giving them plenty to dig through;
- Making absolutely sure there is plenty of space on roosts, at waterers, at feeders and so on, so they don't have to compete;
- Rearranging the coop at the same time you introduce the birds. This more or less can help make the coop a more neutral area, because everyone will have to re-establish territories in the "new" space.
Let your flock free range! Your flock will be far too interested in the prospect of all the worms, pebbles, bugs and weeds they can get their beaks on to bother with one another. They won't go back in the coop until dusk, at which point they'll be settling in for a night's sleep and won't be so motivated to harass one another. (Though we don't recommend you do this until any newcomers have spent at least 2 days inside the coop, so they know it's "home" and to return there every night. Otherwise you may have a runaway bird on your hands!)
