Of course!!! I would leave the eggs for a few days after hatch day even if they don't hatch, the last thing you want to do if Crack the egg and see a little chick still absorbing a yolk or blood vessels
A very powerful flash light or they sell candlers but they can be expensive. My incubator has a built in candler but your using a broody so I don't know
If they are far enough along it will appear black you may see *some* movement if you keep it perfectly still and in a completely dark room. Is the whole egg black? Can you see the air cell?