I WOULD NOT put them together yet!!! We raise chickens until they are old enough to live outside (feathered out) and then sell them. Of course we keep some for our own flock. I have pullets of mixed ages with a few weeks between then but I would not suggest putting the little guys in with the full grown hens until they are close to the same size. Even when they are first introduced I would make sure that they have a safe place to get away form the bigger hens. If possible it would be better if you are introducing a larger group of little ones to the bigger ones. Let me explain!!! If you have 5 hens, I would not introduce just 2 little ones, introduce 5 or more. Strength in numbers! And just keep an eye on them to make sure that they are not picking on the little guys.
We keep the day old pullets in a wire kennel lined with chicken wire. When they are about three weeks old they go into the "nursery" where they will stay until they are about 8 weeks old. Then they go outside to a pen, next to our hens and will stay there until they are about 4 months old (or when they look ready!!) then we will put them in with the hens. We usually have 15-25 hens and will introduce the same number of little ones. There are many places for them to hid. KEEP IN MIND, when you do introduce them they might get picked on a little. THis is natural. They are just establishing their "pecking order". as long as one isn't being beaten up they should be fine.
Good luck