On the point of rearranging active battle members. I would like to add a bit more of what I found in my game.
If I send an active party member (I shall call this party member 1) home from the dungeon, I can replace the now empty slot with another member (I shall call this party member 7). But if I send the now at home member back in to the dungeon, the slot where member 7 is at get replaced by member 1 without me trying to rearranging it again. Which is why I think it's some kind of a bug.