I have raised zebras and , mostly, giant danios ; that is too large for eggs . My guess would be disease "dropsy". What I would do is wait for them to die and make sure no other fish also have the problem. Dropsy does not seem to be very contagious.
I've had a problem with my Danio too. I determined that she just ate too much and was bloated. I recommend decreasing food and seeing what happens before jumping to conclusions of a deadly disease. But I do recommend separating your Danio just in case and decreasing food.