Chickens often sit until the eggs hatch, not until 3 weeks has gone by. Hopefully just removing the eggs will break her. Do you have other chickens? All you need to do is pick eggs so she doesn't have anything to sit on. A broody hen is only a problem if you can't pick the eggs fast enough.
I have the same problem. My eggs under my hen never developed and she is sitting like lock down. I am wondering if I take her eggs or just lock her out of my brood cage. I don't want her to loose her gentleness with my kids. She previously let them play with her chicks
One SLW is a roo, the other is probably a pullet. It does not look like any are barred rocks. Like mentioned above, rocks have yellow legs, (or is it just the lighting) but the birds are pullets. Way to dark for cockerels. As they grow they may get clearer barrs.
Can you separate them and listen. It sounds like you know what to listen for. I think some of my KCs got Drake feathers before you could tell by head color. I have had similar issues with to many male birds. 3 roos for every 2 hens and only 4 hens out of 15 in my ducks last year.
You count the days of incubation not the days since eggs laid. If you mean the hen started sitting on them at different times count from the ones with the head start. The chicks will roll the unhatched eggs at lock down.
The still air allows different temps at different spots. When I used a still air I rotated egg location . I realize that is information for next time. I think now you should take the eggs out of the Turner and go into lock down. Any that hatch will roll the other eggs. Hope you get several...
I would expect removing the chick to work. There is a good chance she will stay and wait "sensing' the other chicks even if you don't remove the chick. You could always finish them in the incubator if you have it warmed up ready to go.