Competitive, OK...
...first things first, your Natures are poor on everyone except Luxray, so some rebreeding would likely be necessary to make the most of this team. Secondly, Giratina is banned 9 times out of 10 for being Uber, so he probably will need to be replaced. As for specifics, here's a looooooong list:
Here's a basic set for Luxray:
Luxray @ Choice Scarf
Adamant/Lonely/Jolly/Hasty
Intimidate
- Spark/Thunderbolt
- Ice Fang/Return
- SuperPower
- Crunch
Standard Choice Scarf set, to bypass Luxray's horrible Speed and make the most of its great Attack stat. Spark beats Thunder Fang by a seemingly insignificant 5% accuracy, but 5% better is still better, so Spark is the best physical STAB for Luxray. You can use Thunderbolt to punish stuff like Skarmory, but losing your most powerful STAB attack is quite a cost (and no, don't run both.) Ice Fang is breeding only, but Luxray really, really needs it - if you really don't want to rebreed, Return is the only other option really. SuperPower gives great coverage especially with Crunch, and since Choice sets switch in and out a lot, Intimidate will be spread across the opponent's team and SuperPower's stat drops will be removed. Adamant/Jolly for Spark, Lonely/Hasty for Thunderbolt.
- Houndoom will likely need a re-breed. Counter + Nasty Plot (Egg Moves) instead of Heat Wave and Embargo with a Focus Sash held works very nicely, and can usually guarantee one KO from Houndoom. Either Modest or Timid Nature works best.
- Crobat's Nature is horrid, and Fly is not good competitively. A rebreed will get you a STAB'd Brave Bird to use on opponents, which works wonders for Crobat. Cross Poison is fine, and X-Scissor works well to take out Psychic-types who may try their hand at taking you out. Pursuit is also viable, as is Hypnosis/Substitute, but you'll lose out on Brave Bird should you go with either of these - your choice.
- Lucario...hoo boy, I'll try to make this short. Iron Tail, even with STAB, is poor thanks to its terrible 75% accuracy, and its coverage is rendered obsolete by Aura Sphere. Lucario can go either physical, special, or mixed here and perform well in all three of those areas - you'll need to tell me which area you want to lean towards for me to go into any real detail with this one. Detect and Rock Climb, I will say though, are of no use on Lucario and really need to go.
- Empoleon can drop Waterfall for something like Grass Knot. Agility is a great Egg Move for Empoleon to have (rebreeding only, once again.)
- I've already mentioned Giratina being banned most of the time, so I'd try and find someone else to replace him for competitive purposes.
That's all for now, hope that helped.