2 Hens...1 Box

So I am pretty new to this chicken thing and have a kinda odd question. So I have 5 roosters and 8 hens all in a decent size pen. Recently my husband and I let them start collecting eggs, and one decided to finally sit(it's been about 7 days she has been there now without moving).
Now she is still letting the other hens come and continue laying eggs in the same box she is sitting in(this just happens to be their favorite box to lay eggs). Anyways, a neighbor gave us a couple eggs to put up under her(about 2 days ago), and he told us today that his started hatching today!
Now my question is, if the eggs that we put under her(from the neighbor) hatch in the next couple of days...what happens to the rest of the eggs that don't hatch? Will this throw her off in any way cause she has been sitting for less than 21 days?
(There is also another hen that just started to share the nesting box and not moved for the last 3 days...in the same box!! Will she possibly continue to sit on the eggs that are left behind?!?)

In almost all instances a setting hen will leave the nest within 36 hours after the first chicks hatch. Staggered hatches under broody hens are a disaster waiting to happen.

What would you suggest I do!?
The original hen to sit in the box(MamaDukes/about 7 days) wasn't even laying eggs in the boxes(if at all)! So we found it strange for her to SIT on the eggs that were in the box!
But once those eggs hatch and MamaDukes goes on with her babies, what happens with Queen(the other sitter/about 3 days) and the rest of the unhatched eggs still in the box being sat on?

Since you've got eggs with different hatch dates, and two hens sitting, I'd split them up. Move one hen to a different nest (night would be the best time) or a separate cage and give her one set or the other. Leave the other hen in the original nest with her eggs.
Have you been collecting the newly added eggs each day? If not, you might want to remove them to give the original eggs a chance.

We havent tried splitting the 2 hens, ill suggest that to my husband.
As for collecting the new eggs..nope. they wont let me. Even when they get up for their little stretching/walking around, if i enter the coop they will rush back to the nest && cover the eggs...

You really need to collect the new eggs (and marking the eggs intended for hatching with a Sharpie wouldn't be a bad I dea so you can keep track of them).

If you don't get them, they'll keep accumulating until she can't cover them and none/most of them wont hatch. Reach under her and grab those add ons. If she's mean, wear some heavy gloves and a long sleeved shirt, but definitely get them to give the eggs the best chance of hatching.

Update
So my husband and I have been really observant the past few days, and the other hens weren't laying in the box. They were just sitting for MamaDukes & Queen to get up and walk around(they found another box to lay in). As for the eggs and the 2 hens in 1 box...we have seen 3 babies(so far) and it seems like MamaDukes(original sitter/darker brown hen) is just hatching the eggs, because Queen has been the one to take the little ones in and out if the box, to the food and water.