Like MeGa_SePtile2 said, Diancie is indeed banned in the Battle Maison. I would recommend getting another Fairy type Pokémon, such as Sylveon:
[email protected] Helmet
Ability: Cute Charm
EVs: 252 HP, 152 Special Defense, 106 Special Attack
As for your remaining team, I think you should cut Togekiss out. Having more than one Pokemon of the same type can be to your great disadvantage. If you want a great Flying type, I'd say you go for Either Hawlucha, Dragonite, or Pidgeot (if you want to mega evolve it).
Then the final Pokémon on your team... it should be a good Pokemon that will fill in the weak points in your team. Personally, I think you should have an Electric type. How about Electivire?
Ability: Motor Drive
EVs: 252 HP, 252 Attack, 6 Speed
I really hope I helped you out in some way!