You can download as many skintones in a range as you want. That just means more variety in the chilluns when they are born/NPCs when they are generated.

Ok, this was kinda confusing to me too. If you, for example wanted to download Pixie Flirt (my fave skin) if you download the geneticised version it will be available for babies in the game and to be chosen in the CAS screen. Or, You can download the NPC available version and then Pixie Flirt can show up on townies as well as babies but it won't be available in CAS. Yes, I am 100% certain that NPC available skins can show up on babies, it does on the baby from pregnancy number 3.

But remember, you cannot go and download Pixie Flirt from MTS2 and stick it in your game as it will conflict and then none of the three skins will work.
I forgot to add, I use
this default set as well. Save for the alien skin, because I use Enayla's unholy collection at MTS2 as defaults for that.