I have tried various methods harem, female rotation, male rotation and my best results are having each males setup in a tub with females being added weekly and removed when visibly pregnant to be place into an individual birthing tub where they stay until the babies are 5 to 7 days and than placed in communal nursing tubs. During the first 5 to 7 days the babies skin is very fragile and when females fight over the babies it leads to losses and I breed for maximum production.

I use concrete mixing tubs (9 gallons ones) and have 3 females with the males in rotation (one female go out one goes in), as far as nursing I have 3 females with their babies in the same type tubs, more than that and it is too crowded, once the babies are 3 weeks old the females go back in rotation and babies are raised until they are 6 weeks max if not fed before that time.

Now when I did male rotation each males would rotate between 3 tubs each, spending 2 weeks in each tubs.

So as you can see both of those methods work well one I do not recommend is harem, this means the female are breeding back to back being pregnant while nursing and it really takes it's toll on them very fast impacting the babies and litter size.

If I was in your place I would likely have 2.12, with the males rotating between 3 tubs each, and have another rack for growout and holdback.