You raise them up for about 4-5 months in their own pen, and when they are about the same size, you slowly introduce them and let them fight out a new pecking order. You can search "integrating hens" and find other's experiences on the subject.
You can keep them in the same house but I'd use something with smaller holes, like 1/2" by 1/2" hardware cloth to seperate the two different age groups because chicks can get there heads through the holes in the chicken wire and it could be a problem.