i think you should leave them until they have hatched, as if you try to look under her, she might get a bit feisty, and can do a lot of harm to the chicks,so just wait it out a little i would suggest.
so, i had my brown hen sitting on 15 eggs , brooding them, some of her them were her's and some not. About 14 days into the 21 day
hatching process i came home only to find my frizzle hen sitting with her, she was laying fresh eggs in the nest daily but i didn't know and i couldn't remove...
you can gradually introduce them meaning place them in the bigger cage with a smaller cage with them, so therefore this could introduce them better as there could be no damage to them, then out them with them, there might be a little pecking at first but it will get better.
if i were to breed a great laying hen and a more meaty rooster that comes from a line of poor laying hens, would they offspring lay like her mother or like her father's line?
also if the hen lays brown eggs and the rooster's lines lay where eggs, when the offspring becomes older what colour eggs...