You may want to boost all three girls’ HP and the DKs’ Strenght and the WM’s Magic.
Once you kill Mindy, focus your assault on Sandy.. Followed By cindy.
I dont know why your having any problems with the sisters, they were extremely easy for me. What level are your characters?
I also see, that they have no weaknesses. Goodluck!
*I took out some parts of the FFX-2 Strategy Guide and posted it here, i hope its okay*
If they’re doing Delta Attack, it sounds like you’re not focusing hard enough on getting one of them out of the battle. As soon as even one is down, Delta Attack is out as an option for them. Pound away until just one is down and then go for the others. Mix Elemental gems on Alchemist if you have it. If you want, you could also switch into a special dressphere and that should be enough to knock them down hard.
P.S.: You’re bucking to really annoy me bad with these thread titles of yours. It really helps people if you use thread titles that actually describe what the thread’s about. Just calling this thread "Aeon" doesn’t really say much about it.