Suggestions wanted: who should I take to face the Elite 4?

[Lady Vulpix]

So I've finally reached the Pokemon League. Again, I have too many Pokemon and their levels are too low (currently 53-54). I do intend to raise them a bit more before I face the E4, but I will still have to choose 6 out of my team to face them, so it would be interested to see what your thoughts are.

My team is the following:

Delphox
-Flamethrower
-Will-o-Wisp
-Psychic
-Shadow Ball
Notes: faster than lightning, but highly vulnerable.

Charizard
-Flamethrower
-Shadow Claw (may switch to Dragon Claw, even back and forth depending on who I must challenge)
-Wing Attack
-Slash
Notes: good stats overall, can megaevolve but that's a double-edged sword as it makes him weak to Dragon and Fairy type attacks.

Pidgeot
-Return
-Fly
-Featherdance
-Roost
Notes: fairly good at both attack and defense, pretty fast but not fast enough when her opponent's levels are so much higher.

Butterfree
-Sleep Powder
-Quiver Dance
-Bug Buzz
-Psychic
Notes: Sleep Powder may save the day, if it can be thrown in time and lasts long enough. Speed is good but again, levels don't help here.

Vaporeon
-Surf
-Blizzard
-Shadow Ball
-Swift (not expecting to use this move here)
Notes: good Special Attack, great against multiple opponents but that's not the case here, naturally high HP, other stats are... OK.

Snorlax
-Yawn
-Protect
-Body Slam
-Earthquake
Notes: Yawn+Protect make him a good alternative to Butterfree's Sleep Powder. HP-tank with high Attack, very slow but may attack first thanks to Quick Claw.

Kangaskhan
-?
-?
-?
-?
Notes: may get to megaevolve at some point, I haven't tried that yet. Good stats overall, but I haven't found a convincing moveset yet. She's usually the one who uses Strength, but she's also quite good in battle.

Roserade
-Toxic
-Leech Seed
-Venoshock
-Giga Drain
Notes: super high Special Attack makes Venoshock and Giga Drain effective in battle. He's already defeated a Greninja (with Ice Beam) and Xerneas in a random challenge. My main concern is that type matchups do not favor him against the Elite Four.

Aurorus
-Ice Beam
-Ancient Power
-Icy Wind
-Nature Power
Notes: Nature Power is better than I had expected, but Ancientpower is not that good, it is only there because I needed a special Rock-type move (because his Special Attack is better than his Attack). Icy Wind might help with Speed issues, even though it makes my ears ring when he uses it.

Steelix
-Iron Tail
-Dig (or maybe Earthquake? Earthquake is stronger, but Dig can be used strategically).
-Payback
-Double-Edge
Notes: Double-Edge has no recoil effect, and she can actually take advantage of her low speed. Huge Defense, good Attack.

Lapras
-Surf
-Ice Beam
-Rain Dance
-Body Slam
Notes: I was unsure about Rain Dance, but it has proven to be helpful sometimes, especially against opponents who benefit from other weather conditions. His stats are all quite good, especially HP.

Lucario
-Aura Sphere
-Dig
-?
-?
Notes: I've been rotating the other 2 moves. He has good Attack and Special Attack and can megaevolve, but he can hardly take a blow, so he's the main candidate to not face the Elite 4.

Ditto
- Whatever moves the opponent has.
Notes: Imposter ability, fully EV-trained for HP, great against higher level Pokemon. I didn't think so at first, but I'm seriously considering taking it.

So... suggestions (and reasons)?