when to let chick in with my girls

Last year I introduced my two new POL chickens to my established hens, free ranging in a smallish area.  The top hen really went for them.  When I took her away, the next in command went for them.  Eventually I took all three established hens out and over the next 4 weeks re-introduced them to the new girls.  Eventually it all settled down.  No doubt I did it all wrong and someone will tell me so and how I should have done it (I hope so).  I would be very careful and don't turn your back until you are sure.  Good luck, let us know how it goes

16 weeks, i didnt realise it would be that long before they can go together
gonna have to make the babies coop that is in the big girls run a bit bigger, it wont take 5 16 week old chickens!
just have to sweet talk hubby for a bit more work to be done