To beat the ghastly trio take them down in order of apperance as you met them along in the dungeon.
Meaning, when you are at the boss room, take down Goliath, Atlas then finally Titan.
This is due to Goliath randonmly summoning monsters when his HP is low, and if you ignore him too long and suddenly land a big hit on him, he'll summon nonetheless..
Atlas 2nd to his net being hard to deal with especially if you got Goliath still alive and has his summons out. If you get caught you're gonna die if Goliath and his summons haven't been dealt with. He also casts haste on himself when his health is low, but due the generally clumsy nature of the bosses he'll spend most of his time running up and down then actually doing damage. You can continue to go for the kill or move on to:
Titan is last due to his only real threat being that he cancelss your buffs, although this could turn to an advantage for you, where you buff and let him debuff you, while he does this, you can use a heavily damaging attack which have long start up times to put the hurt on him. Note, that only if you got the MP to spare of course.
Raikai lvl 60 Grand Master
Dirgel lvl 58 Wrecking Ball
Spamlina lvl 50 Gaia