They get Smite Evil, which does grant a damage boost.
Paladins cast from Wisdom, and O-Chul's Wis should be high enough. If there's something keeping him from casting it's him not having enough class levels.O-Chul can't cast spells. He has abysmal Charisma score and we know he multiclassed into Paladin. He doesn't even have a mount.
The fact that most of them blew their saves doesn't mean that paladins in general don't have high saves, as they get their Cha as a bonus to saves. (So O-Chul's out of luck.)Quite the opposite. Paladins have an abysmal track record with saving throws in this story.
Thanh fell to Tsukiko's domination. The entire saphire guard went down due to Xykon's insanity symbol.
O-Chul himself was paralyzed by Xykon. O-Chul and Lien both fell to Serini's poison.