Yes, that is normal behavior all around. A hen weans her chicks when ever she wants to. This year I've had two broodies raise chicks, one weaned hers at 3 week the other at 4 weeks. In past years I've had some broodies go over 2 months. There is nothing really consistent with the timing and not always with the method either. I've had some sleep with them at night but leave them on their own during the day. And I've had some take care of them during the day but abandon them at night. But with most it's a clean break when ever it happens.
How big is your coop? How are the roosts set up? My chicks don't roost on the main roosts with the adults until they mature enough to force their way into the pecking order. With pullets that's usually about the time they start to lay. With cockerels, who knows. If they try before they are mature enough they normally get beat up pretty badly by the adults. Until then they look for a safer place to sleep. That might be on the floor, it might be on or in something else, like your nests. I integrate all the time and put a juvenile roost a little lower than the main roosts, higher than the nests, and horizontally separated from the main roosts to give them a safe place to go that is not my nests. My coop is big enough I can do that.
I still have had some juveniles totally leave the coop to sleep. I usually toss them back into the main coop after dark and lock them in until they get in the habit of going in themselves. Sometimes they catch on pretty quickly, sometimes it takes weeks.
I also have a grow-out coop at the far end of the main run. If it's empty I may lock them in there at night until they start sleeping in there on their own. When they mature enough I move them back to the main coop. That may be your solution, especially if your coop is fairly small. Give them a safe predator proof place to sleep that is not your main coop, at least for a while.