Ideally they should be in quarantine, away from your chickens, for at least 2 weeks (preferably 1 month) to make sure they don't have any diseases that could spread to your chickens. If they are young, they should be raised to at least 4 months old, so they are closer in size to the full-grown hens. After quarantine, I keep them separated by wire, but visible to each other for 3 weeks so they can feel more like a "flock", then allow supervised visitation until I can trust them to not draw blood. If you can free range them together, that is really helpful. It sounds like a lot of work (separate coops, runs, etc..), and it is, but it will keep you from chicken tragedy.
