Are you referring to the level 5 ghosts on the first level, in the corridor to the arena?
Spiritual resistance does get a boost from intelligence, but agility / speed would help more than that. For now, skip the ghosts and clear the rest of the corridor. The mini-map will show if a cell's occupant is hostile or not. That should get you up another level, and the stat boost should make a noticeable difference.
If you have one warrior and one archer or mage, you can attack, then have your warrior run away when his health gets too low, while the other character continues to attack from a distance. How long it makes sense to go toe to toe with a ghost depends on how much damage you are doing / taking and how many potions you are using.
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