Hi, welcome to the forum. Glad you joined.
We all have different facilities and management techniques. It's no surprise that we use different methods and get different results. I'm a firm believer that the more room you have in the coop and outside the better.
My brooder is in the coop. They go in there straight from the incubator or post office. In essence the chicks grow up with the flock. At five weeks I open the brooder door and walk away. That's it, it is over. But in addition to them growing up with the flock I have a large coop with hiding paces, a large area outside where they can stay far away from each other, and I have the weather where they can be outside all day every day. If yours are not raised in the coop and you don't have that kind of room I would not suggest this method.
Some general tips for integration. House them across each other with wire for a while so they get used to each other. Give them as much room as you can inside and outside. You can improve the quality of your room by adding clutter, basically giving them places they can hide under, behind, or above. Do not force the into tight places thinking they'll fight it out and learn to get along. That's dangerous. Instead be as patient as you can and let them work things out at their pace. If they want to avoid each other, let them. Provide widely spaced feeding an watering stations. That way the older cannot bully the younger away from food and water.
