I would suggest Adamant for Flareon, especially since it have access to Flare Blitz in XY. It's Spatk is pretty useless anyway, and it needs the extra power to be useful, and its also not fast enough to sweep in any case, so a tanky variant is preferred.
Lucarios nature depends a lot on what variant you are running since it can be both special and physical. If you want a physical one use Jolly, or use Timid if you prefer a special variant.
Here is a physical moveset:
Lucario
Jolly Nature
- Bullet Punch
- Close Combat
- Swords Dance
- Crunch
Here is a special moveset:
Lucario
Timid Nature
- Aura Sphere
- Hidden Power [Ice]
- Nasty Plot
- Dark Pulse