I had two blue ORPINGTON gals go broody a few days apart; the second joined the first in the big, covered kitty litter pan / nestbox. Then the buff ORP decided to join them.
I don't know how they breathed - the box was STUFFED with Orpingtons, feathers smashed against the walls and inside of the lid, 3 sets of beaks and eyes peering out through the opening, chittering ominously at any passing chicken. Or dog. Or cat. Or me.
One chick hatched, and one of the blue orps claimed it. The other two hens were "aunties." Then that chick died. Two more hatched, and each of the two other moms took over a single chick, each. Except sometimes they would trade off, and one hen would lead two chicks, other times it was the OTHER other hen.
I don't think it was very safe for the chicks, so next time this happens, I WILL attempt to separate the ladies.