Once they are all the same size, you should be able to integrate without any issues, though the younger ones will probably always be the lowest in the pecking order. I've found that age, rather than size is usually the determining factor on a hen's position in the flock. I have a little game hen who is so tiny, she is the size of a 6-week-old chick, but she is above many much larger birds, in the pecking order.Whew ! Welcome to summer, Danz, I don't envy you at all with all that work in this heat .I have the newer chicks out side next to the big girls and some of the EE's are sparing with the grown-ups thru the fence.I'm having doubts about getting both flocks merged together . That's making more work than I was hoping for ,can't imagine what some of you have to do with larger flocks.
In my flock, they are so used to newcomers that there is very little pecking or bickering. I can throw a new batch of 4-week-olds out there, and the mature hens just take it right in their stride and will only peck a youngster occasionally to put it in its place, if it is being especially cheeky. But if you have a flock of older birds that is not accustomed to newcomers, it is probably best to wait until they are closer to the same size.