Equipment like ribbons, fire, coral and angel rings.
anti-dragon weapons (dragon lance or dragon's whisker).
Not only about rapid fire or dualcast. be well prepared with all the elixirs you can and have good reflexes, in case of using phoenix downs.
one of the post-game bosses, is no joke.
the other one, is more about luck and careful planning when to attack. all-or-nothing, if you want some risk and reward, because that boss can be healed, when you are applying the wrong element.
another possible equipment... reflect rings.
a healer, summoning (optional), time magic, zeninage is not recommended (replace with another skill), blue magic (can avoid some headaches).
jumping can help you with not suffering a fatal blow (or total defeat and turn the tables in your favor).
revive from chemist can help too.
anyway... every mastered job -counts-,
making a good difference and conquering them.