standard UI conventions for this sort of game is for the numbers "1-N" (N=6 in this game) to select characters, and "=" to select all characters. Function keys are mapped to actions for individual characters, corresponding to the order in which icons are shown above the character portraits.Problems with this are.......
You want to keep your eyes on the screen and not look down at keyboard constantly though.I feel this is the reason that in videos of POE the player has the mouse pointer running all over the screen and most of my IE playthrus have been done with pointer instead of key binds.
Having to look at keyboard for every character choice and then for every character order is not good for a relaxed gameplay session.You could leave hand on keyboard and memorize where the keys are by feel but that contorts your hand quickly.Most will choose to play by running the mouse pointer all over the screen.So in order to command a character you move pointer from top right of screen down to the lower left/choose a character/chooses an order to execute and then move pointer back up to upper right of screen to select the recipient of the chosen order,back and forth 6 times.With the WASD you simply press W to remove the mouse travel.The pointer simply moves over the character portrait area to allow a quick character and order command and then simply release W and select the recipient of this order and repeat.Its very efficient and makes for a more enjoyable experience.
That said a way to make choosing 1-6 and the Fkeys feel more intuitive is to give us ability to use SHIFT/CTRL/ALT as modifier keys.So with QWEASD as the keys to individually select each toon by pressing SHIFT these same keys now function like the Fkeys.Even better would be to allow us to bind Middle mouse button as the modifier as that frees the left hand to more easily access QWEASD keys,no contorting required.
Maybe someone can think of something better.....