Two ducks 1 nest

Anyone ever encounter muscovies sharing a nest box? There must be thirty egg's in there and they've been sitting on them side by side for getting close to 20 days.  I don't have any rational for why this would be a problem if they seem to be cool with it. But I can't say I know what will happen when each thinks she's thee mom for whoever hatches.

I can support their shift worker policies, there happy as can be together, I just wanted to know if it commonly occurs in flocks.

Two of my Mum's muscovies shared a nest, now they share the ducklings. I imagine the sharing thing would reduce, not enhance the duckling's chances since they're kind of bewildered anyway!
They hatched a LOT of ducklings between them, but have managed to seriously whittle down the numbers. It seems standing on their heads is a popular method of infanticide....
It was their first clutches and Mum's first muscovies, so I don't know how standard sharing is.

Yep first clutch, one of the 2 lost her first clutch to crushing duckling hip's with her feet. Now her and a henchmen are gang brooding a pile of egg's and I'm not big on more hip crushing. I tripled the size of their nest boxes after the incident, but then they filled it with double the ducks.

Now that I've witnessed the result's, it's shocking how much better two ducks are than one. They hatched out 8 squeek monsters, and they can't keep up now that there getting on two weeks old. At first there were scuffles between the two and another mom with her flock. Everybody picked rogue duck's out of there groups with toss em in the air precision. I didn't know they could work so well together as a team, one huddles with the group the other goes and finds the stragglers.