I assumed Riku and maybe mickey helped them move SDG to Twilight Town.
No no no, you're all wrong, here's what actually happened.
here are a few things to consider
1: There are multiple pods both in Castle Oblivion and Twilight Town, so it wasn't a matter of moving the POD, just a matter of moving SDG to Twilight town
2: The mansion is more or less a safehouse for SDG while they sleep, since keeping them in Castle Oblivion is reckless as organization XIII knows where it is.
3: SDG are fast asleep inside the pods, so I doubt that merely opening them up would wake them, while we wouldn't know if there is a time limit for how LONG they will be asleep outside the pods, we can assume that it is long enough for a corridor of darkness warp.
With those three things in mind, it can be implied that Namine and Diz just carried them through the corridors of darkness and shut them inside Twilight Town's pods. Not much to it really, since we see them using them.