I would be worried if they are dying and I wouldn't say it's normal. The red mama on the picture looks sick(Is this the one with possible columnaris?)
When I kept my fry in a breeder box, I did water changes and cleaned the bottom everyday(there is almost no flow from the main tank to keep the water healthy. I didn't lose a single fry, even a premature batch survived and they couldn't swim for a good while after birth. If you have plants, moss balls, put quite a few in the breeder box. They'll be less stressed, also some microorganisms on the plants will serve as snack for them too and the plants will help filter the water in between water changes. But I would look into them being sick too if they were together with a sick fish.