Pick up the eggs and listen to them. If you hear nothing, feel no movement, or if they slosh, they are duds. I think you should be happy with the four you have.
If you have an incubator, you could try that. Because if I remember right, you said 4 eggs were added late. Your choice, but even if...
Well a bit off topic - did the chicks hatch?
But as to the barebacks, I have found they bother people more than they bother chickens. Do she still love him, hang out with him? If so, you really don't have to do anything. If she is hiding in the coop, then you need to separate him.
That will be fine. Are you pretty sure on the date? By tomorrow, take her off the nest and check the eggs. If it sloshes - they are no good. At this stage - there should be piping, or even a faint cheeping. Sometimes you just don't have any that make it. Dispose of the eggs and put fakes in...
Just leave her be! She knows more about being a chicken than you or I will ever know. Just leave her completely alone, do not disturb her, or check on her or try and peak, do not try to help.
People with the best intentions, want to be part of this, and help it go smoothly thinking they can...