Let's review the procedure as outlined on the FAQ page. It is crucial to follow each step exactly, none of these are optional.
-Vacation your sims from World A in World B. Have them stay anywhere temporarily, even an empty 10x10 residential lot is fine if there is no Base Camp.
- Have them purchase a vacation home. You may need to change the one you wanted them to move into to Residential-(Player) Ownable to make this happen, and you may need to change it to Community (No Visitors Allowed is fine) in between to get the change to Ownable to stick.
- Have them move into the intended home from where they were originally staying.
- Invoke Traveler's Change Hometown on them.
- You MUST save (as), quit all the way to the Desktop (or Origin), and reload as you are prompted to do at this point otherwise the game remains in a fragile state.
That's it, the household is now permanently residents of World B and travel back to World A (the correct one) can be done or sims can be pulled into World B as the FAQ says. If you skip any of these steps or do not do a Change Hometown, then you are really still in vacation mode even if it doesn't "feel" like it and either travel back to World A will indeed spawn a new version of that world or other unexpected things can happen like you can't get back into World B if you travel away from it again.
When done properly as above, using MC to pull in sims from World A should not break their relationships nor their family trees but even if it does that can be fixed up with MC commands. What tends to do that is inviting them over as guests and then marrying them or forcing the otherwise mini-sim versions of them to become residents. The MC Add Sim > Homeworld command pulls in full-fledged sims, not mini-sims. You may still see the original copy of these sims back in their homeworld on the greyed out portion of the relationship panel, but those will get resolved eventually and can just be ignored if Overwatch and ErrorTrap are in play.
There is also EA's Move to New World function that essentially destroys the original world going forward. Traveler is supposed to protect the original world when that function is used instead of the vacation fake-out method above, but it just isn't very reliable and things still tend to go wrong. I never use it.
The nhd file hocus pocus is not part of this procedure. It is for when you have two totally different saved games and you want to connect a world and its sims that are in one game save with a different world and its (different) sims that are in a different game save. If the same sims are represented in both game saves, you will get some unreliable and strange results. It is also useful for when you have edited World B, where sims might move to, and wish to use that one as the new target so you don't have to keep redoing the world edits over again, it's not for replacing where sims have come from.
