Counter slow with haste, its better than using dispel imo. Cecil should start off as a support character, casting shell and protect on everyone. Rosa should heal and haste, Rydia should be spamming -aga- spells or Bahamut (if you have him) and Edge and Kain should focus on attacking. Don't bother using Edge's ninjutsu, it sucks against bosses. Kain should be fine as is. For a defensive game, keep the Defender on Cecil, for an offensive game, use the Avenger.

I find Barbbarricia is the nastiest of the four fiends. The same strategy used to beat Cagnazzio and Rubicante still apply hear.