I hope I am missing something here.

This seems kind of odd, but I can't figure out the button to cycle to next party member, without to having to use the mouse to click on the actual character or portrait.

There doesn't seem to be any assignable action for the simplest key function of "select next character in party"
under keymapping -> Game
Target nearest enemy: \
Target next enemy: TAB
Select previous target: backspace
Player List: P (doesn't seem to do anything, for MP maybe?)

under keymapping-> Misc.
Toggle Group Selection: Mouse 5 (toggles the rest of the group "active" but with different symbols; the originally selected character keeps the main activity symbol under it and is still active when group is toggled off.
Select Group With Mouse: Mouse 4 (allows marquee box selection of multiple characters, leaving the originally selected character with the main activity symbol. If you select multiple characters that were not already selected, then the character higher on the portrait chart becomes "main active")

There doesn't seem to be any keymappable action for the simplest "select next character in party".

a little progress...found a reddit thread mentioning F keys. F keys are not shown in the GUI/keymapper.
According to the manual F1-F10 are "possess" companion
SHIFT F1-F10 are "target" companion.
Problem is, if you hit F1 twice you first possess and then target character 1 as well. Then if you hit F2 you possess character 2 but character 1 is still lit up as well as a target. Then you have to take the mouse and right click on the target to clear it.

What a mess.

It would work much better for me in single player to completely disable "friendly targeting" and have 1 button to cycle through "possess next companion".

If anyone knows how to change any of that (maybe it has been done in the .ini directly with no gui support?) please let me know. I want to play through the game, but this just painful.