The roosters won't be the issues it's the hens. After the chicks have full feathers to withstand the weather, put them in a holding pen inside the coop. This will allow the hens to acclimate to the new birds. After two or three days let the new chicks while you are watching. "Should be ok"...
I just built an 11'x21' flight pen. The sides are 6' tall and the netting is 14' in the center. It has a 4'x6' brick "hut" that is 6' tall with roosts, bottom half has doors that can be closed in cold weather. I have raised ringnecks and silvers in the past. Now raising bobwhites for dog...
