I'm watching Nature and they just mentioned it. Seems the ladies get fertilized elsewhere. If they both lay eggs they eject one from the nest as they only raise one chick at a time. But they can alternate which one gets to pass on their genes (discovered with genetic testing of the ejected eggs). It's a fascinating show. Now they are on to a male fish that the ladies all like because he raises all their eggs. He gets so many eggs that smaller male 'assistants' join the nest, getting to fertilize some of the eggs. Earlier they had a creepy nest of gregarious spiders (rare in spiders) that share caring for each other's egg sacks. Lots of material here for my world building.