Earliest Sign Eggs Are Developing? (take # 2)

I posted a big long description in the hatch a long thread before realizing I put it in the wrong place so I will just be posting the pertinent information here.

I have a pen of 2 frizzled bantam cochin hens with a silkie rooster.
They all liked to sleep in a beat together.
I didnt think any of the hens were laying.
Yesterday I found my smallest hen brooding in the nest. I bribed her off the nest with a treat planning on throwing a couple eggs under her.
Imagine my surprised to are a doubled stacked nest full of eggs! She layed down again before I could count them and today not even treats would get her off.
Now I am wondering if any of the eggs are still good.
What is the quickest and safest way for me to determine if any .pf the eggs has a chance?
I considered just leaving them all since she is covering them all but I have other fertile eggs I want her to hatch if these are duds.

 

So we got paid some money we were owed and so my Darling Hubby bought me an incubator and an automatic egg turner!
I set it up last night and have been adjusting it since then.
Today when I went out to get check the birds mama was off the nest getting a drink! I quickly grabbed all but 4 eggs and took them inside to candle them. There were two different sizes of eggs and I left 4 small ones under mama. When I candled the eggs I brought inside I found the smaller eggs were looking better then the big ones. I think I will switch 4 big ones for the 4 small ones later tonight or tomorrow morning.
That poor little tiny half naked banty was laying on 18 eggs!!!
I can't get a hydrometer until Saturday so I just put a tiny splash of water in the incubator for now. I am in Ontario and it is pretty humid.
All the eggs showed some development when candled!