Two broody hens together, and broken eggs?

We have two broody hens in a ratproof coop. They take turns in sitting on the eggs that they laid between them as they were all gathered together by one of them. Two have hatched successfully and the chicks are thriving. However I have found two eggs outside their nest, one about three feet away and both were broken with a dead chick inside. One was almost fully formed and the other was still red and tiny. Should I take one broody out and just leave one in? Will it make any difference to the chicks doing this? Why are these eggs so far from the nest and how did they get there? Please can somebody help as I don't want to lose any more chicks.