Ruby Weapon(pathetic boss, that is weak against the most simplest(is that a word) spell).
Since he has Knights of the Round it should be alot quicker, but Knights of the Round is not needed, any Non-Elemental spell will do, but well take Bahamut as an example, since it's better with a summon anyways.
First off, if you already found out the little trick of killing your party upon the start of the battle, use Phoenix alone.
Once the other characters are alive, and have one character with W-Summon, Hades, Bahamut, and HP Absorb equipped to Bahamut. Have someone with Mime equipped(if all three then good for you). Have everyone have a Ribbon(because the status effects he causes) equipped, and if you have one, have that character with everything said here equipped.
Cast W-Summon, Hades and Bahamut. Mime the attack continuously until Ruby Weapon is dead, as he will rarely get any attacks on you because he will be stopped most of the battle, and you will finish the battle with full HP due to the HP Absorb.
Emerald Weapon(harder boss, still a wuss)
Equip everyone with the most powerful armor you can first off, you should have two Zeidrich(I think that's how to spell it, I haven't played in forever.
Have every character with Cure, and each character with a one powerful summon spell, but don't stop at one, have a few if you want. To make the battle alot easier, equip someone with Phoenix and Final Attack, but do not let them die first. Don't bother wasting the times you can cast your spells until he opens the four chambers where he attacks and drains MP, as soon as they open, cast a summon spell to destroy them. If an attack he makes kills someone, then revive them, but if not, then cure them.
This boss isn't really as hard as everyone makes him out to be, you just have to conserve the times you can use your summons so you can destroy the four chambers each time they revive and open up.
But anyways, using these strategies the enemies should be easy.