Adding new chickens to existing flock

[IreneTBW]

I just recently lost my rooster and would love to get more little chicks and grow them, my question, when they will be bigger how to add them to other my 5 chicken team that already 1 year old, are they older one will pick up on smaller one, how soon i can try to put them together

 

[Cyprus]

I have always put my new chicks in at around 18 weeks. However, I have heard of better success when chicks are raised within sight of the main flock since day 1, and allowed in at 1 week.
They should have a place to escape to with an entrance only big enough for the chicks, if this is done.