Leaders and units - who casts what on whom?

[Nagot Gick Fel]

baboune said:
I was wondering if a leader casts support spells on his troops primarily or if it targets any group?

The latter. As soon as you enter combat, whoever 'owns' a squad counts for absolutely nothing until the battle is over.

Let me give you an example: A Coral Queen commands 2 Groups of units, and a Deep Seer commands 1 set of units.
In combat, does the Coral Queen casts Fanaticism on one of the 2 sets she commands?

This is a poor example as Fanaticism affects all friendly squads on the battlefield . Your Coral Queen will cast Sermon of Courage on whoever needs it.

what group is first selected?

Depends on a lot of factors. Usually it's the one that'll benefit the most from the buff, or the one with the toughest units.