My two silkies have done that the last 4 or 5 times they've set eggs, if one goes broody, the other goes broody, right on the same nest. And they raise the chicks together as well. I have 2 bantam cochin hens that have brooded and raised the same chicks once or twice as well, though the older hen usually takes the babies away, and the other is left with nothing
However, the younger one is broody right now, all by herself! If she has any luck with these eggs in this crazy weather, she will get to be a mama all on her own
ETA: The second time the silkies went broody, both hens and their 2 chicks sat on the eggs, then the whole family (2 hens, 2 8-week old chicks, 5 newborn chicks) would all parade around the yard together...silly birds!