Mystery egg and multiple broody hens

[VonSFarms]

Good morning everyone I hope this is on the correct thread as this is my first post. So 2 weeks ago my husband found 2 white (looking chicken eggs) on the ground at our childrens school. Having been at the school the day before he knew they had just been placed there. He called me and I told him to bring them home. 1 egg was cracked with what looked like a tooth mark pretty badly while the other was untouched. I have a mixed flock of Dominique's, Duccle's and silkies so someone is always broody! We put the egg under one of my Duccle's who is broody and 19 days later the egg is viable, moving and veiny so my questions are:
1. Do i sepreate the Duccle and her egg from the flock bc I have 2 other Duccle's who have been switching off egg duty with her?
2. We have ducks that free range and sleep in the same big run with the chickens could that be an issue?
3. I have baby chickens coming the week after this egg hatches (fingers crossed the hatch is successful) do I sepreate the lone chick and put with the new ones or try to get the new chicks to be with the baby chick and it's momma?
....I will say that yes I am certain it's not a snake, alligator or other type of animal egg that could unleash the Cracken on my flock!!
Any help is appreciated from all of you amazing feathered flock lovers!!

 

[NatJ]

1. Yes, you should probably separate the one hen and the egg/chick from the flock, at least for a few days. After that, it will depend on how they all behave, and on how much space there is. The hen will want to keep the other chickens away from her baby, and she can only do that when the space is large enough.

2. Ducks will probably be about the same as the other chickens: the hen will want to keep them away from her baby, so there needs to be enough space for that. (For example, if she wants them 20 feet away, and if the run were only 10 feet across, you should expect problems.)

3. About the new chicks that are coming: If they hatched within a day or two of when this chick hatched, you may be able to get that hen to adopt them too. (I would figure it by hatch date, not by when they arrive in the mail.) If the new chicks will be more than a day or two younger, you might see if one of your other hens will adopt them--you say some have been switching off sitting on this egg, so maybe they've been broody long enough to accept chicks?

If this baby bird is not a chicken, that could affect how well the hen can raise it, and whether you can add other chicks to this brood.