I think the general idea when introducing/reintroducing chickens is to put them out where they can see each other for a few days, but where they can't attack each other... so separate off part of the run, or put a small cage in the run, etc.
And then if you can let them range around the yard a bit while letting them mix for the first time, that helps. And if you give them a distraction, such as some mulch or leaf litter and treats to scratch up when first introduced that tends to help also. And if a fight breaks out have the garden hose out, and give them a slap of water, to tell them to behave.
I think yours are plenty old enough to do some or all of that.