I am a bit concerned about the broodies' eggs for that reason! There has been so much activity in that nesting box I am not sure the eggs are getting properly incubated, but we'll see. Last night when I went out there, there were actually 4 other chickens squeezed in there sleeping with the 2 broodies.Hope they keep developing. I know some people do but I don't candle broody eggs. About the only thing I ever do is mark them when they come off to do their daily duty so I can remove any volunteers.
I've had co-broodies. About the only thing that goes wrong is they continuously steal eggs from each other. I once had 9 pullets together. 7went broody together and one of the others was a part time participant. They only hatched one chick out of about 28 eggs in their community nest. I try to separate them now but I've yet to have a hen go broody this year.
The beautiful thing about a broody is you don't have to do anything except count the chicks when she leads them off the nest to forage.