Actually I'm not deciding it myself, I'm following PnP, and I was even quite "forgiving" for player's sake because else I should have removed from druids quite a lot more spells (e.g. Doom, Bless, Cloak of Fear, etc.), and clerics should have the incredibly more restrictive sphere system used by Divine Remix.
Only Morninglords of Lathander should be able to cast from the sun sphere, and druids were never able to cast the Cause Wound serie of spells. What's CS by the way?
P.S Cleric should be able to handle undead monsters with their innate ability to Turn Undead (if not, what's there fo