candle them...if there are live chicks you should be able to see some movement...listen to them...the little ones peep inside the shells before hatch...(you probably know that already)...some set the egg in a bowl of warm water and float candle them...if you watch closely if the chick is alive you should see the egg move in the water.....she may be able to hear the chicks, might be why she keeps going back to the eggs....most of my broodys just up and abandoned the remaining eggs as soon as the live ones hatched....I built a special broody cage, just big enough for the nest and an area attached big enough for water and food...and a good stretch..so the broody can't abandon the last eggs until I let her out
You can poke a tiny hole in the air sack end (candle first of course) and take a peek. If you see movement, the chick is still alive. I always check and then open up the egg to reassure myself that i'm not throwing away a viable chick.
I had a broody abandon 9 eggs when the first one hatched early. I tucked them into the incubator, and hatched 8 of them. Of course then I had to raise them, but hand raised Araucanas are really sweet little birds, and I didn't want to abandon them at that point. They were only in the incubator a couple of days. Which reminds me, I need to fire up the incubator and get it stabilized -- my broodies are due Sunday.