Yeah, broken eggs aside. I have never had good luck with it. Everyone seems to have the cutest stories about hens sharing chicks, but the two times I let hens share a nest one or the other killed all, if not most, of the chicks. I am not usually a "softy" when it comes to chickens, but coming outside to new chicks pecked to the bone was pretty upsetting. I separate the one I like best to sit on the eggs and the other goes to broody jail.
As an extra info most of my chickens are pretty hefty types, french black copper marans, EEs, Ameraucana, New hampshires, and welsummers.
I have only really heard success stories from folks that have silkies, but am interested to hear others experiences.