So farm ladies who know all about chickens

Okay, so we noticed that our chickens are laying fertile eggs but they weren't sitting on them, used to if they were fertile they'd have a whole nest within a day and become protective of it. Not our new chickens.. They would lay one egg every day just like normal and leave it and lay another one and leave it. So I found out they were fertile, I put them in the incubator and hatched them out. I now have a second set of eggs in the incubator that are all fertile and are about a 8 days along. I told my mom to stop collecting the eggs.. I told her to leave them completely alone for a week and see what happens. I wanted to see if when they had a full nest of eggs if they would actually sit on them. 

Well, now we have all of our hens sitting on their nest.. Sitting on eachothers eggs, like there's not one nest with only a certain type of chicken egg in it. 

So I am wondering.. Can I put the eggs I have in the incubator underneath the hens outside? Will they accept them or will it cause them to reject the whole nest? What about when they hatch.. They are going to hatch a week earlier than the eggs they are sitting on.. Will that cause them to leave abandon the eggs? This has never happened and I'm really just confused on what to do.. If I can't put the eggs under the hens that's fine.. I just work all the time and I don't want to deal with keeping up with the incubator making sure it's working right and worrying about temp and humidity.