Many people have successfully integrated chickens of those ages. Sometimes there are real serious problems. I cannot tell you what will happen in your specific case.
The younger birds and older birds will almost certainly stay in their own groups until the younger ones pretty much match the older ones in maturity. Then they might form new friendships and hang with each other. But until they mature, they will stay separate.
Some flocks have older chickens, usually hens, that go out of there way to seek out and destroy any younger chicken. Mine don't do that, but some chickens do. I can't tell you what the individual personalities of your hens are. Nobody can.
I have had two-week-old chicks being raised by a broody leave Mama's protection and go stand next to older hens and eat out of the feeder. Sometimes, and usually not for long, the other hens ignore the chick. What usually happens is that one of the hens pecks the chick and the chick runs back to Mama for comfort. This is not an "I'm going to kill you" peck but more of a reminder that it is bad manners for a chicken so low in the pecking order to eat with its social betters. It is still a hard peck and could cause damage or be fatal, but that is not the intent. Some hens intend to kill. I guess it takes a flock to teach a chick proper chicken etiquette.
Younger chickens are going to be intimidated by more mature hens. This has little or nothing to do with size, but maturity. Mature bantam hens will intimidate younger full sized breed chickens that are twice their size. The larger the young ones are the less likely that pecking order peck is going to be as serious, but it can still happen.
Some things that I suggest that might help.
Number one to me is space. The more space you have for them, the better. The younger ones need to avoid the larger ones. A whole lot of the pecking order stuff I see is when they try to share the same space. If the young ones can run away from or just avoid the older ones, a lot of conflict can be avoided. Young ones are usually very much intimidated by the older ones and will wisely try to avoid them.
Part of the intimidation the older ones do is to keep the younger ones away from the food and water. I find it extremely helpful to provide separate feeding and watering stations. Interestingly, if I put out a new feeding station, the older birds will often prefer to eat there first, even if it is exactly the same type of feed in both. But some extra feeding stations gives the younger birds a chance to eat without having to confront an older bird that wants to hog the food.
Make sure you have plenty of roosts. I find the worst time for pecking is on the roosts as they are settling down for the night. This is one time you are forcing them to be in each others vicinity. If you can give them plenty of roost space so they can maintain some separation, it really helps, at least with mine.
If possible, do the integration in territory familiar to the younger birds, not the older ones. This way, the older birds are not as territorial and they spend some time exploring the new territory rather than defending their territory.
Having more young birds than old can help, but I find that integration is pretty much an individual thing. Each chicken has to handle its own integration. With more younger birds, the attention is not always as concentrated, so having more is usually a good thing.
Housing them next to each other so they kind of get used to each other seems to help. If you can house them where they are separated only by wire and throw some feed on the ground where they eat next to eash other, it can help the integration go smoother.
You'll notice I used a lot of weasel words like "if", "often" or "usually". I can't tell you specifically what will happen. We all have different circumstances and chickens with different personalities. People successfully integrate chickens all the time, but occasionally there are disasters. No guarantees on any of this. I wish you luck!
