Is there any way I can get the other two hens out so that my girl can hatch us some chicks?
I typically let my hens hatch with the flock but you have a clear case where that is not a good idea. I don't know what your facilities look like of how many total hens you have. I don't know the best answer for you but will give you some options.
Isolate the broody hen. Build a a pen where you can lock her up and keep those two away. It doesn't need to be that big, just room for a nest, food, water, and a bit of room for her to go poop. That might be fencing a section of the coop around her nest or can be a totally separate pen. Just make sure it is predator proof and does not become an oven in the sun.
Eat those two egg-eating hens.
Lock up the two hens so they cannot get to the eggs.
Also how many days does it take before you can tell wether or not a chick is growing inside the egg?
This depends on how easy it is to see inside the egg (dark brown eggs or blue or green eggs can be harder than white shells), how good your candler is, how dark it is when you candle, and your experience. With white eggs and good equipment you might see blood vessels by Day 3. With some of my dark green eggs it takes a lot longer. Sometimes I'm not sure by Day 7, but my equipment isn't terrific.
