Once the chicks start to hatch you might want to put up a higher barrier on the nest front so they can't fall out....then move them lower when hatching is done.
Is the other hen laying?
Has she tried to lay in the broodies nest?
Do you only have the two birds and the one coop?
It might not be necessary to seclude broody and chicks,
depends on the layout of your coop and the demeanor of the other hen.
Seeing pics of your coop layout showing the nests...