Early on in the game the spell fear comes in handy as does fire magic, so I would recommend that for your mage at least, you spend your points in those realms (air magic gets you a Missle Shield spell later that keeps arrows, rocks and slime or weed spit from hitting you).
The mage also has decent Divine spells (Magic Missles early on, Summon Elemental later) and Earth spells that both cause damage and offer protection (element shield for in-battle purposes and whipping rocks).
Your Samauri is not going to learn spells for a while so put the points wherever you want to specialize. I chose Fire to specialize in for future fireballs and have him cast the light spell constantly to get his skill up (your skills progress as you use them)
Since a Psi specializes in Mental spells, pay attention to that realm and Divine since they also have the heal spell.
Use the Priest for Divine spells and perhaps Earth (for Armorplate).
I do not totally neglect other realms though because you can buy or steal books in order to teach your spellcasters new spells and add spellpoints to the respective realms...I'll add a point here and a point there sometimes for future prospects of having power LOL.
I made some comments in a thread about advancing my spellcasters in another thread...here's the link here if you want to take a look:
Saving Magic