When can I integrate my younger chicks with the older ones?

[atterac]

I have 8 chicks- mix of roo's & hens that are about 5-6 weeks old. We just got 5 more hens that are 2 days old. I was hoping to put them all together in the coop with heat lamp when the babies are 4-6 weeks. They will likely outgrow their current brooder at that point.
Any suggestions would be helpful!
Nicole