The Girls have a total of three nesting boxes available to them. Which should be more than a sufficient number for 6 chickens according to all the research The Man of the House did before building the hen house. And the other two boxes were both completely empty at the time.
So, why in the world these two hens felt the need to crowd into one box at the same time is completely a mystery to me. Apparently they are not familiar with the concept of personal space.