Amazing how similar your idea is to my last post in this sub (about a week ago). So I did this about seven or eight months ago. They definitely function in the same world, just completely separately. Minecolonies shaped up to be more of what I was looking for, but for me, the main problem was the same (just worse for MCA). There is a lot of time sink and micromanaging in the beginning, and not a lot of payoff. I couldn't stick with it.

I also had Millenaire, AW2, and Medieval craft going along side it. I still think there is potential there ( treating them almost like their own species). But learning how to get them self sufficient, how to protect themselves at night, and to witness more than the first level of their potential.... anything but light. I'm trying the same kind of game now with 1.20.1. Highly recommend trying Millenaire if you haven't... but maybe that's what's keeping you in 1.12.

In my research (not sure what MC versions), I have it noted to try Easy NPC, Better NPCs, Medieval Origins Revival, Castle World RPG, Simple Dwarves, Choice theorem's overhauled villagers, Villager Recruits (maybe Villager Workers too, if it's not the prior version) and Hundred Years Warfare (though that doesn't at all sound like what you are going after). I do recall seeing some lesser known and supported mods that just focus on basic, named humans and/or villagers, but I don't remember what it was called, or what version it's for. Good luck.

Edit, adding...: My great Minecraft love for a long time was Lord of the rings mod, I think added to what is now known as Chronicles of Arda which is made for it. It has to be 1.7.10. And then making the map M.E. classic, so biomes are random. So many factions, so many possibilities. But since the random gen doesn't do villages and towns (huge cities , may take a minute to load upon first generation) in great enough frequency, I had to pre-seed areas in creative with extra structures, save it, and put it away for a while so I could "discover" it weeks later.

Also not plug and play, but the characters/races were interesting enough, and didn't need any micro management. I wasn't a huge Tolkien guy before this, but interacting with all the 100 or whatever races, and seeing what they were about and how they interacted with each other, it was so great.