I believe that only foreign EA worlds that were originally intended to be traveled to and back (WA, Uni, Oasis Landing) will appear in Edit Town for transitions while editing, so that part should not be concerning.
Have to admit that I have never traveled with more than 7 sims so I never even thought to ask about that. But if the block is on moving with a controllable household of that size, it sounds like you do not have NRaas Mover in play or it isn't working as expected. The mod is supposed unlock moves and splits with, into, and out of overstuffed households. Allow Greater Than Eight > True is a default setting for Mover. Or it's possible that Mover just doesn't work with vacation homes, but I've never seen that reported before.
I would suggest trying this all over again very quickly with a test game not using the custom world. Load or start one up in an EA homeworld, make some obvious change to it (add a bowling alley or change something that's very easy to see), vacation let's say one or two sims to another EA homeworld (not from WA), go through the purchase and move procedure, Change Hometown, save quit and reload, and travel back to where they came from to see if the already played in world loads with the bowling alley or whatever you have added. If it works as intended, then we have to conclude that the issue is indeed with the custom version of AP that you were starting with.