Appreciated reading this... I am in a similar situation and wonder how you are getting on now?
I have 7x 8 week old chicks (3 polish which are 2 cockerels one pullet, 1x silkie cockerel, 1x Mille fleur cockerel, 1x Miller fleur silkie x hen and 1 silkie x hen) I had 2 frizzle chicks a cock and a hen which a fox killed. So I purchased from a local breeder 2 frizzle hens which are supposedly 12 weeks old but I can't believe that as they ate tiny, about a third of the size of my 8wk Olds. So far they have been living next to each other for 1 week with only chicken wire separating them.
Wondering when to put together, there's a lot of interest through the chicken wire and some pecking too.
I also have 7 big grown up hens..... which need integrating with the chicks too...
They've been living next to the chicks for 4 weeks now