oomiedog - This is a tough one.
I know how badly curiosity can eat at you and not knowing is tough.
I've had one zebra finch who never understood parenting. She didn't understand that she needed to feed the babies. So one by one, they died, but she sat on them and refused to move until finally, I coaxed her out with a chopstick. Poor girl was really trying her best. She just didn't understand.
That's the only case I've seen with a parent sitting on dead babies. One of two things usually happens. They either toss the remains out of the nest or the baby will end up underneath the live babies, where it dries up and gets buried in nesting. (This usually happens when the parent doesn't realize it's died.)
At this young age, they're so small that they don't go off and decompose. They dry up. So there's less concern in that regard.
I've had some clutches who were very loud, very early -- 2-3 days in.
I've had some who were essentially silent for the first 7-10 days, and then found their voices. This seems the most common.
I've had some who never begged until they fledged. Those were virtually all 1-2 chick clutches, so I suspect they were just really well fed and had no reason to vocalize.
They don't just vocalize for the heck of it as it sucks up essential energy resources. Usually it's only when they're hungry. The quieter babies only beg when the parent is actively feeding other babies.
So listen right after a parent comes into the nest. That's usually when they feed. It's super soft for the first 5-6 days. Barely audible.
In your case, I would let them be for now.
If she's brooding dead chicks, then there's really nothing that can be done and she'll come out soon enough. There's really nothing to be gained from disturbing her.
If they're alive, you risk frightening and disrupting the parents sufficiently to cause them to abandon or toss the live babies. So I would just leave them be for now.
The chances of vocalization become more likely as time passes.
Is there any way to put a stepping stool nearby so you can stand on that and peek in with a flashlight, without removing the side wall of the cage?
If you want to try to peek, wait until both parents are out of the nest. You can't see anything when they're in there. Offering fresh egg food and other fresh foods is a good way to get them to come out.
So indeed, I wouldn't pull the cage apart to peek. There's nothing to be done if they're dead and you risk causing problems if they're alive.
I'd make an educated guess and say at least 1 is alive or there is at least 1 unhatched egg. I've only seen that one hen who sat on dead babies. They virtually always toss them, unless they get buried under the siblings first.
And when there are no live babies and no eggs left, they just abandon the nest.
