I don't consider size to be that important. If you have a flock if bantams and full-sized fowl it isn't unusual for a bantam to be the dominant chicken.
I raise chicks with my flock all the time, brooder-raised and broody-raised. Regardless of size, I have yet to see an immature pullet stand up to a mature hen. Usually they mature enough to stand up top a hen about the time they start to lay. Until then the immature run away instead of fight. Maturity is more important than size.
My brooder is in the coop so my brooder-raised chicks basically grow up with the flock. My broody hens raise their chicks with the flock from Day 1 so they also grow up with the flock. I've had broody's wean their chicks at 3 weeks, pretty young but they make their way with the flock. I regularly just open the brooder door at 5 weeks and let those chicks make their way with the flock. They are still really small.
I don't lose chicks to adult flock members, it just doesn't happen. But I have a few things going for me besides the others being used to having the chicks around. I have the climate that the chickens spend practically all day every day outside except when a hen is laying an egg. I have a lot of room, in the coop and outside. The coop itself can get a little tight but it has a lot of hiding places. Depending on the number of chicks and adults I may have between 60 to over 100 square feet per bird outside. A lot of those are young and don't take up much room when it gets down to 60. I feed and water in a lot of different spots, typically three feeders and four waterers. I do not force them to be together in tight spots, I let them work things out. For example, I do not try to force them to all sleep on the roosts together. As long as they are not sleeping in nests and are somewhere predator-safe I don't care where they sleep. I have two separate grow-out coop/shelters that I can put chickens in if I have any issues which gives me some flexibility.
I don't know that any of these are most important, I think they all work together. Nowhere in here is size a consideration for me. I think how much room you have is at the top of the list. If you try to integrate without adequate room it can get a lot harder.
@smfarman I don't know how much room you have so I'm not exactly sure of what to suggest. I'd house the 11 and 12-week-olds side by side for at least a week and then let them together in as much space as I could when I could be around to observe. I'd base what I do after that from what I observed. If they want to stay in separate little groups instead of all getting together, that's fine. They'll get together when they are ready. If someone is getting hurt, separate them.
I don't know what will happen when it gets dark. They may all go back to their individual cages. They may try to sleep somewhere else, either in small groups or together. As long as it is predator-safe I'd be OK with it. I'd prefer them to roam with each other, either in individual groups or all together, a while before I forced them into the same coop to sleep but it's not totally necessary. You can try that the first night after you let them out. If you put them in the same coop at night I'd be down there at daybreak when they are waking up to open the pop door and let them out if they need more room. I do that when I move chicks from sleeping in my grow-out coop to the main coop, often at 12 weeks. Practically always I see after just one or to mornings that there are no issues if I want to sleep in a bit. You may have different results. Don't be afraid to try, just take reasonable precautions.
If you have problems with any of this, keep them separated but where they can see each other a while longer. Then try again. Just be patient.
With the 16-week-olds, I'd include them in all this. Give it a try. It could work out where it is no problem and life is good, especially if you have a lot of room. Or they may need to wait a bit. Go by what you see when you try and don't let what might possibly happen keep you from trying. Often these things go so smoothly you wonder what all the fuss and warnings were about, even if you don't do everything possible. Sometimes you do everything possible and you still have problems. You just don't get guarantees with any of this, that's the way life works. You also don't have any successes if you don't try.
For your basic question, I'd let them see each other for a week and then try. After that go by what you see happening.