Wrath - Zemus cause his creation Zeromous is the enbodiment of of Zemus' hate

Lust - Kefka, cause Kefka had the greatest lust for power (lust isn't just sexual)and he killed more people to get to it than any other. Power was more important to him than anything else.

Greed - Emperor Palamecia, cause he wanted the world even though his empire was grand enough

Pride - I have to give this to Kuja cause his reasonings for destroying all of existence is because existence doesn't deserve to exist without him.

Gluttony - X-Death, who was already the physical embodiment of several forbidden magics needed the power of the ultimate forbidden power in order to quench his "thirst" and "hunger" for power.

Sloth - Sephiroth, cause he never really did his own dirty work (if you don't count the flashback, you only meet the real Sephiroth twice. Once in the "Promised Lands" and later at the bottom of the Crater) He always worked through his clones and Jenova (Zemus also gets an honorable mention but you're only allowed one deadly sin )

Envy - Seymore, who had a terrible life cause of his mix ancestry wished to change Spira but couldn't cause his role was restricted, he tried everything to gain the powers of others to fulfill his own desires.

There, all seven, all different major villians (except for Seymore cause I still believe he was tacked on to the plot)