For a line, you will want Strafe Left for two toons on one key.
In addition you'll want Strafe Left for one of those two toons on a different key.
If you are using ISBoxer, you could make a two step Keymap, with both moving on step 1, and only one on step 2.
With ISBoxer, turn on "Hold any keystroke actions while hotkey is held".

Do the same as above, for two toons to strafe to the right.

On the first button (or press of the button, with 2 steps), two toons move left and two move right.
On the second button (or second press, with 2 steps), one of each pair of toons moves further left or right.