I have had mixed results keeping colonies of rodents (mice and rats alike) together. Sometimes the females will share the rearing duties quite well, but I usually have some loss in subsequent litters as the older babies seem to push out the younger, weaker babies who then starve. Occasionally, there is outright cannibalism.
As an alternative, the most successful tactic for me has been to raise several (8-10) females for each male, keep colonies of 1.4 together, and pull females that are visibly ready to give birth and place them in a "nursery" bin of their own. Once the babies are weaned, the mothers are returned to the colony. By then, new females are pregnant and it just becomes a rotation.
Since females become recptive imediately after giving birth, some people prefer to leave the females in so that they will become pregnant immediately, resulting in higher frequency of litters.
I still prefer the seperation method as it results in practically zero infant mortality and, at least I think, healthier animals. I say this because the babies seem to grow much quicker this way, and the females produce for a longer period with larger litters. To me, this makes sense as there is less strain on a nursing female that is not depleting her resources to both nurse and gestate at the same time.
I'm sure there are many successful methods, but this is what has worked best for me.