The answer to your question is not easy, so bear with my long-winded reply.
Everything depends on how and where you keep your birds. I seem to recall from your earlier postings that you will be keeping them on your allotment, so that probably means just one house.
If birds are truly free-range, i.e. not in a run, it is fine to let chicks which have been hatched under a broody out with their mother at 2 to 3 weeks old - mother will see off any unwanted attention from other hens. This is what I have done for the past few years.
Chicks from the incubator can be outside, but in an enclosed run of their own, when they are fully feathered and the weather is warm enough. This allows the other hens to see them and become accustomed to them without being able to attack them. When they about 15 weeks old they can go out and fend for themselves. They will automatically go back to their own house at night.
If birds are confined in a run, mother and chicks cannot safely be with the others and young incubator hatched chicks will not be safe until they are virtually point-of-lay (18 to 25+ weeks depending on breed).
The way to introduce new hens to a house of older birds, it is generally advised, is to put them in with the others after dark. Having short memory spans, when they wake up in the morning the older hens will, hopefully, think the newcomers have always been there. But you will need to keep an eye on them.
Sorry to be so long winded - but who said keeping livestock was easy (just a great pleasure)?
I hope you can find something helpful in the above.
Best wishes
Alan
Cred air o bob deg a glywi, a thi a gei rywfaint bach o wir (hen ddihareb Gymraeg) Believe one tenth of what you hear, and you will get some little truth (old Welsh proverb)
Good answer Alan. I also make sure that the young ones get enough to eat, having a separate food dish for a while helps, but I had to stand guard until they were brave enough to just get stuck in with the older ones.
You might think that your reply is long winded, I Don't.
Thank you for much your very informative reply it takes the fear factor out of raising young incubated chicks Now that I know what to do in the future I feel much better