You may want to wait longer. Wait until they are almost the same size as your current hens (if you can)
If you do not have a place to keep the chicks until they are at least 3 months, make sure they have a place in the coop to get away from the hens. Like a roost that only they can get to. Last summer we had 5 chicks that we added to the flock once they were fully feathered because we didn't have a big enough place to keep them. It didn't go well at all. I had to keep going out to feed them and give them water so they didn't starve. They at least had a place to get away. They used the roosts and the tops of our angled nest boxes that the other chickens were too big to balance on. Once they hit 4 months, it was like the magic number. Now they can all jump down and eat whenever they want, with no problems whatsoever.
So if you can, my advice would be to wait longer. If that's not an option, be prepared to go out quite often to give them feed and water during the day.