For the Neochu, I ended up giving 2 of my characters the Random Instant Chain ability. My third character was Fang with a Genji Glove equipped. After they scored a instant chain on it, it was fairly easy to finish off with Highwind. Mop up the lackies with Blitz.

Also, for both the Neochu and the Adamantoise, equip all three characters with Gaian Ring. They make the battles far more managable. I didn't use Sentinels for either.