Why would you use Mega elixers with Crono, Robo, and Ayla? Robo has a three party heal, and Ayla has kiss for desperate situations. I usually use Triple Kick, Confuse, or Uzzi Punch on the left bit, then foucus on the middle bit until the right bit turns its power off. The once the right bit turns its power off, I do Volt Bite and Shock.
I make sure to have the Prism Dress on Ayla, Safe Helm on Crono, Crisis Arm (Not Terra!) and Haste Helm on Robo. Those items basically garuntee ultimate victory.