This is all very normal behavior, if the hen's poops are runny and if the pair has increased their feeding, these are signs that she's in the mood. Some good advices are given by SeanM which you may take note of.
Just my curiosity, are they a proven pair? Since it will be their first clutch at your home, I would not recommend a lot of meddling or efforts to check the eggs and all, let her brood the eggs and if the chicks do hatch, let them feed the chick(s) for the full cycle i.e. till the chick(s) weaned because this is a learning curve for the birds themselves, they should know what is required of them.
In future, however, you can take the chicks out on or about 20th day and hand feed them to raise hand tamed birds. You can do this while the parents are feeding the chicks by taking the chicks out during the night (when the hen is out of the box, and close the nest box opening) and give them the feel of some handling with humans and place them back in the box after about half an hour or an hour of socializing.
Good luck