"merge" minecraft worlds

Question

I run a Minecraft server.

I want to duplicate the server, and run two servers now. Server A and Server B.

At the moment, world A and B are identical.

I want to let some people (players A) onto Server A to break and place some blocks.

At the same time, I let other people (players B) onto Server B to break and place some blocks. Players B are nearby to where players A are in Server A, but not so close as to be building in the same blocks themselves.

After both groups of people have finished building and destroying parts of the two different worlds, World A has things in it that World B doesn't, and vice versa.

How can I create world C that has both all of players A's changes and players B's changes?

E.g., if players A built a house in world A, and players B built a house somewhere else in world B, world C should have both these houses.

Answer 1

If they are far enough apart, you can just overwrite the region files of one world with a part of the others. Region files save a part of the world that is 1024x1024 blocks big.
So if for example players A build on X coordinates lower than 2048 and players B on X coordinates higher than 2048, then you can just copy the region files called r.[number ≥2].[number].mca from server B to server A and confirm that you want to overwrite.

Region files are found in
.minecraft/saves/[world name]/region for the overworld,
.minecraft/saves/[world name]/DIM-1/region for the Nether and
.minecraft/saves/[world name]/DIM1/region for the End.

Answer 2

While there is no way to do this officially (That is a method provided by Mojang/Microsoft), I found a post on Reddit mentioning that you could use MCEdit to combine the changes (I have given MCEdit Unified as MCEdit is out of date)

While this may get more complicated depending on the changes, it may prove at least successful as a program to straight up merge the worlds could potentially have issues if two structures are in the same place. With MCEdit, one would be able to cut the interaction from one world (A house built, a machine etc.) and paste it into the other one. The structures can be moved about to make room for each other, so you don't get some crazy shenanigans like a Super Smelter going straight through the barn you just built because you both had different ideas.

If you need help with using MCEdit, I'm almost certain a quick Google will bring up sufficient help for at least this task.

Hope I could have helped!