You can't thier spots since you are standing there and thus they can't stand there unless they are spawned on the same spot
Any skill which has a targeting circle can be used to move a cell which is already occupied by player. This works best on area skills such as hammerfall for example. When you cast a skill on a certain square your character will move along a straight line to the nearest walkable cell where it cn cast the skill. When player is on a cell the cell is still considered walkable thus you can stop there.
Not really i have tried it and it worked but when i was on my other char i saw my first on another square while my third char which was there when i took that spot shows
that i am still in that spot when i walked down and return with the third char i saw my first char in another spot too
thus i can assume it's just impossible