My suggestion is to chain Mirror Knights in the Feywood. An hour of those guys can net you about 200,000 gil so you can easily gear up to better prepare for the last stretch of the game. It sounds like you might be a little under the usual level at that point in the game, but that doesn't mean it's not possible, it's possible to beat the game at extremely low levels with proper preparation, so I would concentrate more on that. Mirror Knights are probably the best way to go.

If you just want to beat the game, focus only on three characters and neglect the rest, you won't need them.