On trader update. If not moving, check if other trader on same tile. If there's one, check if it's running a move order. If not, move to another tile in the zone (so 2 traders don't move at random only to possibly end up on the same tile again). Issue: none.
UI Fix:
On select click. If 2 target are within X pixels of the click, and that one of them was already selected, switch to the other. Might also fix select issues on world map and shit. Issue: probably doesn't cover all cases.
I was only able to select one of them because the other was being obscured.