Just level your characters up and use things like cerberus and carbuncle to get good stats on your party before you use carbuncle though i think you should use haste shell and protect etc and if that doesnt work or you can't battle to level up then i'm sorry to say but you're stuffed oh and just to let you all
shiva-get off computer at beggining
quazacotl-same as above
ifrit-get at the fire cavern
siren-draw off elvoret at dollet
diablos-use the magic lamp
carbuncle-not sure
pandamona-draw off fuijin at balamb town
tonberry-fight about 20 tonberries
cactuar-go to the island beneath esthar and fight the little head poking out of the ground.
doomtrain-you need malboro tentacles steel pipes and remedies then use the soloman ring(don't know how many of each though)
bahamut-fight on the way down to ultima weapon(bottom left of map)
eden-draw off ultima weapon.
oh and cerberus-fight in galbadia garden.
you know when you fight ultimecia one of her forms if you fight her long enough then another target appears and you can draw apocalypse off it.