Ok to start of, yes the eggs turning white are dieing. Don't worry unless more than 1/4 of them turn white. As for the others, some hatch earlier, while others wait until they are more developed in the egg to hatch. You want to have some water movement but not enough that it tosses the tads around. Make sure there isn't a yucky film on the surface of the water. Mortality rate is going to be very high in the wild or captivity, their is no way around that. Personally I don't think you can feed 20 toadlets. Keep in mind that in the wild they would eat countless amounts of insects every night. You should let the majority go. Also let the parents go. When you found them the female was carrying the male to a spot to lay eggs, which wouldn't have been the creek you found them by. Well best of luck with those tadpoles, currently iam raising 200+ wood frog tads.