Ideal: two lists, non-draggable, with the subtasks/supertasks - and a button to split them, add the other tasks list, and make the whole thing drag/drop.
Easier: Just add the 3 lists from the add view.
Compromise: Add the 3 lists, toggle showing the other tasks list with a button.
Ideal: two lists, non-draggable, with the subtasks/supertasks - and a button to split them, add the other tasks list, and make the whole thing drag/drop. Easier: Just add the 3 lists from the add view. Compromise: Add the 3 lists, toggle showing the other tasks list with a button.