Candle the eggs for development. Give the more mature looking eggs to hen #1 (original hen). Give the less mature looking eggs to hen #2, or toss the less mature looking eggs and start hen #2 on fresh, set at the same time eggs.
Best is to move both to isolated broody nests. Second best is to block off that nesting box with the original hen and move hen #2 to a new, isolated, location, and see if you can settle her there. Move at night, nest and all, if possible. Otherwise set up nest, set eggs, then move hen.
This is the reason it is best to isolate and segregate hens....or....at least set eggs on the same day, marking them with the date set with a black marker, then remove subsequently laid eggs if it is a communal box. In laid back flocks, and assertive broody gals who give no truck to anyone, this can work.
If you have tussles over a nesting box, you will need to move or blockade as eggs tend to get kicked out or crushed.
At the very least, definitely plan on throwing up some sort of blockade on day 18 with hen #1; otherwise, hatching chicks will get trampled by the foot traffic for that popular nesting box. (I know of that which I speak).
Let us know how it goes.
LofMc