I've investigated the recent disappearances. In addition to T'Challa and Shuri, going through the records in the TARDIS' console, there have been five other disappearances, Kate Bishop, Logan Echolls, Veronica Mars, Mel Medara, and Jinn.
There doesn't really appear to be a reason why they were sent home, and judging from the data we were able to pull, they were sent back to their home universes. It would also seem that when someone is sent home, all of their belongings vanish, and their rooms are cleared out. Out of these seven, Shuri and T'Challa were here the longest, the others weren't here very long.
So, apparently, we
can get home, there just doesn't seem to be any control over how and
when we get home. Like being pulled here, it appears to be done at random by the TARDIS herself.
I know Martha and myself will be looking into this further, but Martha's the TARDIS expert, and this is still something that she's never experienced.
For the time being, we'll keep looking into this, and if there are any more disappearances, maybe we can try and pick up on a pattern or something. But so far, it appears to be at random.
I'll try and answer any questions as best as I can, but Martha probably has better answers than I do.
In the meantime, I hope everyone's enjoying Kalos. If anyone wants someone to go exploring with, I'm here.