I had ducks and chicks of the same age living together for about three months. The ducks were much bigger early on. They all got along, but were together from a couple of days old.
Most of my eggs were "bad" or questionable, but we will never know. Some visiting children decided to open the incubator AND mess with the thermometer. They dropped it in the fan and didn't tell anyone. We are a bit peeved and sad.
I have one that looks like the second picture of day 10. Dark on end with a darker spot that I can see in it. Some of the others just look dark at the one end. I'm hoping my candling is just not powerful enough.
I also have some that look pretty clear. I expect these are no good at this point.