My Kepler Bb people don't have formula and in fact my much higher tech Kepler B# people don't have formula either.
So when they have babies it is for the baby a breastfeed or die situation. No matter what they have to do(connect a breast pump to a nasogastric tube in the worst case), the baby has to be breastfed from birth to 2 years.
Solids start anywhere from 9 months to 1 year so that is longer than human exclusive breastfeeding.
There is a similar situation going on in my generation ship, no formula at all for the aliens or for the humans.
My concern is mostly with multiple births. While yes, twins, triplets, and quads can all be easily breastfed in a way that all the babies get an equal number of feedings at each breast, quintuplets and onwards are not nearly as easy to breastfeed in a way that all babies get an equal number of feedings at each breast. And from septuplets onwards, more than 1 woman is needed to feed the babies.
Now yes the rates get exponentially lower as more babies are added to the group of multiples but it is still possible. That exponential decay is even more exponential when you don't take into consideration separating a morula into individual eggs(which can happen naturally but is rare), multiple ovulation(which again can be natural but rare), and other fertility increasing therapies(IVF is essentially high tech, forced, multiple ovulation) and just look at the results for naturally conceived babies.
So while twins overall may be a 1/80 chance(taking into consideration fertility therapies and naturally conceived twins), the chance of naturally conceived twins is much lower.
Anyway, there are several ways to go about easily breastfeeding these high multiples(over quads). Here are those ways and what might result:
Method 1: Wet nurses
This I view as the best method because:
1) Wet nurses can lactate for years and years without becoming pregnant in those years and years
2) Not every adolescent or young adult female can breastfeed a baby either due to some defect, low milk production genetics, or maturity reasons, or simply because they don't want to.
Method 2: Young women induced lactation
This I view as second best for breastfeeding multiples. This is very similar to the Wet nurses method in that it is induced lactation. The only downside to this that I can see besides defects and genetics is that not every young woman of the same age has the same degree of maturity. And of course there are those that simply don't feel like breastfeeding.
Method 3: Timing the feeding for each baby
This I view as a bad method because a baby can feed for anywhere from 5 minutes to 45 minutes per feeding. And if you time all the feedings to be the same length for each baby just to make room for sleep for both the multiples and you, bad outcomes are going to result. The milk supply could dry up if you use this method. And inevitably you are going to end up with babies that are still hungry after their feeding and even worse, underweight babies like this:
The baby on the left is of a normal weight or maybe even a bit overweight. The one on the right though is underweight. A skinny baby is never good. It means one of 2 things:
1) It was born at a low birth weight and hasn't caught up
2) It hasn't been eating as much as it should for whatever reason(low milk supply, illness, even pain alone can lower the appetite and potentially cause the baby to get underweight)
Method 4: Infanticide
Basically this infanticide would be where women or men with high multiples kill all except 4 babies. To promote survival, these 4 should be the top 4 in terms of birth weight.
While this does make breastfeeding a whole lot easier, it also has a lot of downsides. Here are those downsides:
Breaking of the law
One of my laws for people on Kepler Bb is no murder of any kind(suicide, homicide, infanticide, etc.). If someone decided to kill all except 4 babies that person and possibly even the mother of that/those killed baby/babies and her surviving babies would end up in prison.
On the generation ship, the aliens take an even more drastic approach towards crime. For them crime = death of both the victim of the crime and the criminal. So infanticide on the generation ship would mean not only no father if it was the father that killed the baby/babies or someone else besides the mother and father but also no biological mother. Luckily children are never killed by the aliens so the baby/babies left from the infanticide would go to young women and have adoptive mothers
There are other downsides such as emotional stress but this breaking of the law is by far the biggest downside to this infanticide.
So how should these super rare cases of quintuplets and higher be handled? I personally think that either one of the 2 induced lactation methods(wet nurses or young women) is the best way to handle it if it is too much for the mom but is there a better way that doesn't risk underweight babies or breaking the law? Remember, there is no formula so that isn't an option.