Auron, Rikku, and Tidus
Tidus would cast haste on everyone, Rikku would get to attack twice after haste was used, so I'd usually have her do a spell and steal an item from the enemy (I made sure she had all of Lulu's and Yuna's spells so she was my support and offensive magic), and finally kill whatever was left with Auron. Battles usually didn't last over 1 full turn with how everyone was set up (and boss battles were always incredibly fast).
Tidus would cast haste on everyone, Rikku would get to attack twice after haste was used, so I'd usually have her do a spell and steal an item from the enemy (I made sure she had all of Lulu's and Yuna's spells so she was my support and offensive magic), and finally kill whatever was left with Auron. Battles usually didn't last over 1 full turn with how everyone was set up (and boss battles were always incredibly fast).