I think it depends more on your strength/abilities per character more than who you use specifically. You may not be strong enough for the area. Do you evenly use everyone in the party? Switching out can be done every turn; see who your strongest fighters are against the monsters there and use them. I haven't played FFX in months so I don't even remember what was at Macalania, so I can't help specifically.
But.. Is there any area you can return to right now right before this one? Try strengthening people there. And make sure you heal people, too! How quickly are people falling?