Tink can go with the Vitamin Quest's approach & make the MC build some kind of nursing centre, after that the girls should be able to give birth infinitely instead of limits by the amount of child's bed in the house.This can probably easily be modded in, just remove the check that lets them give birth. Personally I'd rather continually knock them up then enjoy their new status for a bit before doing it all over again, and keep the cycle going indefinitely.