You can, but it is risky. As Elmo said, a huge consideration is room. If they have a lot of room to get away and not be trapped in a corner, they odds of success will be much higher.
As important as room is, other things also come into play. What is the personality of your chickens? Some flocks have chickens that seek out and destroy young chickens. Many don't, but some do. It is usually a hen but it can be a rooster. Until they get the opportunity, you won't know if you have one or not.
Chicken etiquette requires that chickens lower in the pecking order defer to chickens higher in the pecking order. Size is not the determining factor as much as the spirit of the individual chicken. But one thing is very clear. Mature chickens always outrank immature chickens. They are very jealous of that position and enforce it by pecking and intimidation. The young chickens will be scared of the older chickens, as they should. It is not that it is just good manners, pain and suffering are in their future if they aren't afraid.
There are two kinds of pecking. One is the "I'm going to kill you" pecking by the "seek out and destroy" chickens. Truly dangerous. The other is the pecking order peck. This is not meant to kill or injure, but to enforce proper chicken etiquette. It is still a hard peck and can cause damage or death, so there is some danger associated with this type of peck, especially if there is quite a bit of size difference. As long as the chick has room, it is usually not a big deal. But if the chick is trapped in a corner and cannot get out of the personal space of the older chicken, it can develop into a kill condition. The younger chick cannot get away yet the older chicken keeps pecking it to tell it to get away.
Many broodies wean their chicks by the time they are the age of yours. Its quite possible chicks that age can be integrated with a flock. There are risks. Some things I think help you reduce those risks, other than space. You are already doing the house them close to each other trick.
Have separate feeding and watering spots. Three is better than two, but it depends on how much space you have and your set-up. One way older chickens intimidate younger ones is to keep them away from food and water. If younger ones go near the food and water, the older ones peck. Having more than one feeding and watering station reduces the opportunities for conflict.
At that age, yours may still be sleeping on the ground in a pile instead of roosting. If you can give them a separate sleeping area, such as in the corner you have then in now, whether they roost or not, you can reduce an area of potential conflict. Mine are especially vicious defending pecking order rights on the roosts, and often there is not a lot of room for them to get away. So I suggest try to provide separate and ample sleeping arrangements, whether they are in the same predator-proof area or not.
Do not leave them locked in the same coop after they wake up, especially at first. Open the pop door as soon as the sun comes up. It is real easy for them to get trapped in a corner in a coop. Once they get used to each they will probably work out a routine where the young ones get up on the roosts and the older ones get on the ground for the food and water, but give them that chance to separate as soon as possible. After a while, you will reach a point where they can be left locked in the coop together, but I suggest that you don't start that way.
You can try it at this age. It might work out well, but then it might be a disaster. There are many things that go into it. I do suggest when you try it, that you be around to watch and intervene if necessary. Integration is one of those risky times that sometimes it is great and you wonder why you were worried, but then sometimes it is a disaster.
Good luck!!!