When I was a kid we had pet Gerbles. When ever they had a litter – we would try to get them out of the cage before the male ate them. However, I do not remember if it was to keep his dominance in check or a type of “population control”.
Do you remember the book Watership Down? (Great book!) In the beginning there is a part about how they are becoming so over populated that the females begin to “absorb” the litters before they are born.
I just found this on a Mississippi State University site:
Rabbit Cannibalism
This situation can be caused by a variety of conditions like when the does become excited by an environmental change or when the nutritional status (usually water) is restricted.
Eating young often occurs when varmints, household pets, rodents, or some other unusual visitor enters the rabbitry soon after the doe has delivered her young. The eating of young is an instinctive survival response of the doe. Restrict all animals and visitors from entering or roaming near the rabbitry. The problems often occur at night when rodents and varmints are more active.
Here is the Link: http://msucares.com/livestock/small_animal/cann.html
Although – I have never heard of siblings eating each other.