Thank you for the additional information. It's common for the first litter to die or for the mother not to take adequate of them. Some baby rabbits are born with genetic defects that don't permit them to live past a few days. But, it would be unusual for a whole litter to be affected unless the parents were very closely related to each other.
Becoming too cold also kills young rabbits, but that's probably not the case, either. However, I would turn off the fans because a draft, even a warm one, can easily lead to illness. If you use the fans, place them where no draft goes toward the rabbits. A mister can also lead to trouble because bacteria can grow in the water that is then misted. Too much humidity is not good for rabbits. Baby rabbits are not as likely to suffer from heat as are adults. Babies actually need to be kept in the 90*s for the first couple of weeks. The mother adjusts their temperature by piling more fur on them or by removing some. No additional heat is needed.
With the circumstances you've described, what seems most likely is that the mother rabbit isn't producing enough milk. There are a few does that produce very little or no milk. Without nourishment, the babies will only live a day or two. With inadequate milk production, they will live longer, but fade. If your female is one of these does that don't produce adequate milk, it's likely that the same thing will keep happening. One thing that could result in poor milk production is an insufficient diet. While the foods you are giving are nutritious, this may not be enough. It is usually recommended that a five pound rabbit receive 1/4 cup of pellets per day. A ten pound one should get 1/2 cup. However, when lactating, rabbits need much more food in order to produce milk. When babies are nursing, I let my does have all the pellets they want. You may also want to check the following site for diet recommendations to make sure the mothers are receiving the best possible diet.http://www.bio.miami.edu/hare/diet.html
The other possibility is that the mother is carrying an infectious disease. Being only a carrier, she wouldn't be sick, but the babies could become infected and die.
I would start by making sure the fans and the mister are not problematic, and by giving nursing mothers all the pellets and hay they want. If that doesn't help, the next step is to see an experienced rabbit vet. If the mother isn't producing milk, the vet may be able to determine why and offer some solutions. Testing can be done for some infectious diseases. However, all of this could become quite expensive. Here is where you can find a rabbit vet:http://www.rabbit.org/vets/vets.html
If you have more questions, just let me know by clicking on REPLY. I hope your remaining babies will survive, and you'll be successful with future litters.
(The above answer is intended for informational purposes only. If your pet is ill, you should consult a veterinarian. )