I don't think I've ever tried to change homeworld with Traveler until now so I thought better to ask you guys what's the best way to do what I have in mind. I have a family of husband, wife and toddler and I want to make them go to France, then have the mother and child permanently move there and come back to my original world with the father (I could make them divorce while in France or keep them in a kind of estranged marriage until a later time - but I don't know if it's possible to break up 'long-distance'?). How would I go about doing that? And also I want to make sure the relationship connection stays intact and they're still listed as wife/husband (or ex) and child in the relationship panel.

I'm slightly confused. Do you want to play as the wife in France, or move them out and keep playing in the original world as the husband? If you want to move them out, I think traveling to France with the whole household, using Edit Town to put the wife and kid in a different household and returning home with only the father active should do the trick(?). Only problem is the block on moving actives with Edit Town. I've did it in the Future before to merge a household but I can't remember how I worked around the restrictions.

First Way
Travel the household to France on a vacation. Have them buy a vacation home and move into it (this requires a Level 3 visa for the WA worlds). Send the father back home "early" by phone or computer so that he is no longer part of the traveling party -- he will disappear and be waiting for you in suspended animation back in his homeworld. Invoke Traveler's Change Hometown on the remaining party of two, save as, quit to desktop/origin, reload. The active household will be the mom and toddler, their homeworld will be France (warning, the WA worlds don't typically make very good homeworlds to play, they aren't designed to be), active play will be in France. Are you sure this is what you want?

To get active play back to the Dad and the original world, you will have to transition active play (travel with no one on board) back to where you started.

Second Way
Same as above, but keep the family together at first. When they are switched to France, then travel the Dad back to the homeworld on a vacation and work with him as a household of one to Change Hometowns again. Problem with this method is that he/they will lose ownership of the house they were living in back in the homeworld.

Sorry that wasn't very clear. I want to keep playing the husband as the active family and return with him to the original world after moving the other two out. So that would be the 2nd method I guess, though I'd prefer not to fiddle with his homeworld too much if that's possible...

The underlying problem is that we cannot push sims into foreign homeworld status. We can play them actively and make them citizens of a new homeworld using Traveler's Change Hometown or we can pull them into new (to them) worlds using MC. But unless I am missing something, the husband cannot be part of the actively played household while the Change Hometown takes place without, as in the second method, his changing change permanent residency as well.

I guess you could also try this in the way that Jello02 suggested and just leave the wife and Toddler in France (using MC's Add Sim to add them to a different household, if that's possible), but seems to me that their homeworld status might become uncertain going forward if you do so.

Hmm I think I might try the add sim thing in a test game to see what happens. I just thought of another thing - maybe if I just travel with the mom and child, change their homeworld while there, then do the empty transition with no sims selected back to the original world, select the dad and just have him visit them in France for a while. That should work, right?

Yes, that last one is probably the way I would do this. For some reason I thought having the Dad present at the time of the split/breakup was an absolute requirement, but even for a strict storyline it shouldn't be totally unreasonable that a family of sims might have to travel separately. Maybe they got a better fare or could use up some airline miles that way.

I'll do it that way then, thanks! I'll blame the delay on work-related stuff, it's a demanding job being the emperor of evil after all, you can't always get away from the office/evil lair

I did some testing of my own, and it works, but with some minor hiccups along the way.

Made test save with two Sims. Traveled to China. Right clicked a resident to make him active. Used MC > Intermediate > Add Sim on Sim 2. Right clicked Sim 1 to make him active again. Traveled Sim 1 home. No one was active, but Sim 1 seemed to get home correctly. So I made Sim 1 active, traveled him to China again, and Sim 2 was indeed treated like a resident, spawning in the house that I added her to in the beginning and whatnot. So I sent Sim 1 home for the last time, and this transition went normally, with him being active when the homeworld loaded.

(Hope that wasn't confusing, sorry I fail at grammar.)

I also used a small testing world for the homeworld so it would load quicker, you might possibly need to look for Sim 1 when there's no actives in a larger one depending on where the camera is.