Okay, so I came up with this brilliant plan to be able to move my two new young adults partners into the main home.

I moved a teen and her IF made real to her grandparents home using MC add sim.
No huge problem, the IF made real showed up right away, and I opened the home with MC to make sure she was safe.
My teen was still at her parents home, so I used MC go home and off she went.

I had both YA girls chat up their YA boyfriends and ask them to move in.
That worked fine.

But when I used MC add sim on my active lot to move the two teens back in, nothing happens.

I checked and I have households set to allow up to 10 sims and 3 pets.

There are only 8 sims in my active household and no pets, but it's not letting me add the two teens.

What have I done wrong?

After getting all 10 of them back in the active household, I'm planning on using Traveler to first vacation in my next town and once they're settled in, follow the steps to make it my new home world.

Is that going to be an issue with 10 sims?

Should I travel with just the 8 I have now and try to move the teens back in the new home world?

Check NRaas > MC > Settings > Allow More than Eight Sims. Sounds like it might be False. There is no MC setting for 10 humans and 3 pets, that sounds more like StoryProgression but MC is the mod you are trying to use to overstuff the main household.

Thanks, Igazor!

I've been scrolling through posts and came to that same conclusion, that my setting to allow more than 8 sims was done in SP, not MC.

I don't use the option very often in my active lot, so I was totally puzzled as to why it wasn't working.

So is it safe to travel with 10 sims in the same household, as long as I remember to allow for teen travelers?

That sounds fine to me, but of course be sure to have made saves from safe points before doing so and Save As then quit and reload soon after arrival, etc. in case something goes wrong. I take it you have PortraitPanel so you can more easily keep track of everyone.

I do have portrait panel and you were right on the money with the issue being MC, the allow more than 8 sims settings was set to false.

I made it true and popped both teens back into their Starlight Shores home.

I typically sell the home as they move to the next town, but even with MC set to true, it wouldn't allow me to move to an empty lot before traveling, so I just skipped that part and will sell the home from the new town.

And one of the first things I did in Monte Vista was to change that setting to true!

Thanks for helping me get all 10 of my active family moved to their next town.

Move to an empty lot...that would require Mover, if you were attempting that by way of phone/computer or Edit Town rather than by way of MC. The in-game move and split household functions are not going to recognize overstuffed households as either the source (moving from) or destination (moving to) without that.

And then NRaas > Mover > Allow Greater than Eight > True (which this time it is by default).

This is an example where what can seem like one modded game function, playing with and through overstuffed households, can take several mods to work something close to seamlessly. But you're welcome and glad that's all that was really wrong!