Like you have the space to wait until their full grown LOL! I stick them in with the old ones at about 5 -6 weeks. Heck, Ive stuck 2 week olds in the the big ones, as long as they have a place to hide, they do fine. The 5-6 week olds get chased around and tail feathers get pulled out, but I never had any injuries or fatalities. BUT I do have a large coop & run. And if you have 30, it shouldn't be a problem at all. The big ones will probably be overwhelmed. LOL!
I don't normally stick 2 week olds in with the big ones. Somebody unexpectedly gave me a few chicks last year and I wasn't set up for them, and didn't have time to get set up. One of them got stomped, probably when one of the big ones got off the roost, but the other 4 made it. ( I had 25 big chickens )