I have two questions: 1) Is there ANY way possible I could re-battle..

1. You can not rebattle them. Once you make them faint thats it. If you want them you could always trade with other people.

2. Well, use Dialgas flamethrower to beat the first elite 4 guy (aron)
For the second use a grass Pokemon (seeing as how they are all ground/water pokemon)
For the third use psyduck or empoleon.
For the fourth elite 4 I would use dialga (just to raise him)
Then on the champion use Pokemon that will have super effective hits on the enemy.

I would advise replacing psyduck with a grass Pokemon that is atleast level 50
Raise haunter to level 50ish to actually do anything againt the 4th elite 4 and the champion. And raise luxray to lvl 50.

To bad you only raised empoleon well. You should try to make a well balanced team.

1. Unfortunately, you lost your chance...

2. First, I have to suggest a couple things. One, your team is at horribly low levels, except for, of course, Empoleon. And two, your team isn't the best to use for the E4. You should use these types for the E4: Fire, Ground, Grass, Fighting, Ice, and Dark. You'll see why just now.

For the first member, use a Fire attack against Dustox, Heracross, Vespiquen, and Beautifly. Use a Ground attack on Drapion.

For the second member, use a good Grass attack on all her Pokemon [consisting of Quaqsire, Hippowdon, Sudowoodo, Whiscash, and Golem].

For the third member, use a Ground attack on Rapidash and Infernape. Use an Ice attack against Drifblim [a Dark attack would do good, too.] Use a fighting attack against Lopunny. For Steelix, use either a Fighting attack or a Ground attack.

For the fourth member, use a Dark attack against Mr. Mime, Girafarig, and Alakazam. Use a Fire attack against Bronzong. For Medicham, if you can, use a Flying attack.

And now, we're onto the Champion. Spiritomb seems intimidating because he has no weaknesses and is not affected by Normal, Fighting, or Psychic attacks. And so, your best bet is to use a Dark attack against him.
Against Garchomp, use an Ice attack, and he'll go down in one or two hits guaranteed.
Gastrodon and Milotic need a good Grass attack.
Roserade gets a Fire attack.
And finally, Lucario gets a Flying, Ground, or Fighting attack.

Now, an example of these Pokemon and their [highly suggested (by me, at least)] moves would be as follows:
Fire: Rapidash @ Flamethrower.
Ground (AND Water): Whiscash @ Surf AND Earthquake.
Grass (AND Poison): Roselia/Roserade @ Energy Ball.
Fighting: Machoke/Machamp @ Revenge AND Vital Throw.
Ice AND Dark: Sneasel/Weavile @ Ice (Beam/Punch) AND Night Slash.
Flying: Staraptor @ Aerial Ace.

Question # 1:

The only way to Re-battle the Jirachi trio as they are nicknamed is by an Action Replay the following is the code for Action Replay for D&P:

Re-battle Uxie / Mesprit/ Azelf /
94000130 fcff0000
B21c4d28 00000000
B0000004 00000000
20001144 00000000
20001287 0000000c
D2000000 00000000

Question # 2:

Your team needs to be between lvl 60 - 70 in order to have a good chance to beat the E4 and Champion Cynthia. Here is a break down of all her Pokemon that may help you out.

Elite Four # 1 - is Aaron, who primarily uses Bug-type Pokemon. A
Flying- or Rock-type Pokemon will be valuable in this fight, although
Electric-, Ice-, and Psychic-type attacks are also effective against some of
His Pokemon.

His Pokemon: Dustox lvl 53 / Heracross lvl 54 / Vespiqueen lvl 54 / Beautifly lvl 53 / Draporion lvl 57.


Elite Four # 2 - is Bertha, the master of Ground-type Pokemon. If
You have a Water or Grass-type Pokemon I recommend using it or a Pokemon with water & grass type moves.

Her Pokemon : Quagsire lvl 55 / Hippowdon lvl 59 / Sudowoodo lvl 56 / Golem 56 / Whishcash lvl 55.

Elite Four # 3 - is Flint, whom you've seen earlier in Sunyshore City. He uses Fire-type Pokemon, although really his team is pretty mixed up so be ready to take on a variety of Pokemon types. A strong Water, Fight, Ground, Ice, & Electric Pokemon or those moves types should take out all his pokemon.

His Pokemon: Rapidash lvl 58 Infernape lvl 61 Lopunny lvl 57 Steelix lvl 57 Driftblim lvl 58

Elite Four # 4 - is Lucian uses strong Psychic-type Pokemon. He'll start off with a Mr.Mime, so try and start with a Dark or Ghost type.

His Pokemon: Mr. Mime lvl 59 / Medicham lvl 60 / Alakazam lvl 60 / Bronzong lvl 63 / Girafarig 59

***Champion Cynthia***
Once you've beaten Lucian, heal your Pokemon to full HP. So recommedn you spending some coins and stock up on healing items for HP&PP's

Her Pokemon:

Spiritomb lvl 61 ( Will be her first one out always so be ready)
It doesn't have any weaknesses, actually, so don't worry so much about what
Pokemon you start with in this fight. With it's high Defense and Special
Defense and total lack of weakness, Spiritomb will likely take a few good
Shots to take down. Its offenses aren't that great, though, so at least you
Shouldn't be too threatened.

Gastrodon lvl 60
Its only real weakness is Grass-type attacks, so if you don't have any
Of those, try to rely on using your strongest Physical-based attacks against
It, because it has lower Defense than it does Special Defense. Be careful,
Though, because it has strong moves such as Earthquake, Stone Edge, Muddy
Water, and even Sludge Bomb.

Milotic lvl 63
Is the real pain to take down. It's weak to Electric- and Grass-
Type attacks, although it has the HP and defenses to take a good hit from one
Of them and still survive. Avoid inflicting it with a status ailment, though,
Because otherwise it's Marvel Scale Ability will kick in and raise it's Defense
By 1.5x. It also has Mirror Coat, which is nasty if you use a Special-based
Attack against it, because it will inflict double that damage back to you
(unless you knock it out, of course). Avoid using them if you can.

Garchomp lvl 66
He is a fierce Dragon/Ground-type Pokemon with high Attack and Speed. It
Also has nice HP, as well as decent defenses, making it quite hardy and a
Challenge to take down. It can use Dragon Rush, an extremely powerful Dragon-
Type attack; Earthquake, which is just plain nasty and it gets the Same Type
Attack Bonus, making it really deadly; Giga Impact, which is like a beefed up
Hyper Beam; and Brick Break for a nice, solid Fighting-type attack. Your best
Bet against it is a strong Ice-type attack (beware Brick Break, though!) or a
Dragon-type attack of your own, although otherwise just strike it with your
Strongest attacks and try to keep your HP as high as possible.

Lucario lvl 63
Which you probably haven't fought against since your fight with
Maylene, is a difficult Pokemon to take down due to it's great types. Fighting-,
Ground-, and Fire-type attacks are awesome against Lucario, but nearly
Everything else is really quite ineffective. It knows Dragon Pulse,
Earthquake, Psychic, and Aura Sphere, giving it a very large array of powerful
Attacks. It also has high Attack and Special Attack, as well as good Speed,
But fortunately it's defensive stats aren't so hot. Use that to your advantage.

Roserade lvl 60
Is the last and shouldn't be quite as difficult compared to the rest of her
Pokemon, but it's still a formidable foe. It boasts very high Special Attack
And quite high Special Defense, and it's Speed isn't half bad either. It can
Use Sludge Bomb, which will put a serious dent in your Pokemon's HP. Steel-
Type Pokemon are amazing to use against Roserade.

Good Luck and if this works for you please give my answer a rating. Thanks.

1. Not unless you start a new game... Always save before you battle just in case this happens. And use your master ball for the roaming ones.

2. Just get higher levelled pokemon. Theyre all way too low in level. Except empoleon. It will suffer at the attack of any electric move/pokemon. Raise them. Otherwise you've no hope. Stronger moves help too.

Finding out what Pokemon the e4 and champion have and tailoring your tem and their moves to suit helps. A walkthrough can't really be made for you, because the e4 don't really do predictable things. I assume you wanted something like:

When e4 "trainer" uses their "pokemon", you should use your "pokemon" and tell it to use "move"...

That can't really be done for you, Since at any given time, they may choose a different pokemon... Or different moves. And they might get a critical hit and ko your Pokemon and you mightn't have any revives left... You get my point.

but what you can do is learn what Pokemon they have and go in prepared with suitiably levelled up and move-equipped pokemon. Take in heaps of revival herbs and ethers/leppa berries etc...