Well your team seems to mostly be levelled enough as they are - the Elite 4 aren't that hard. Most of their Pokemon are in the mid 60's, so you might want to train Yvetal and Blaziken up a couple of levels and then you will be fine. As for where to train them, just give them a Lucky Egg and go onto Victory Road. It shouldn't really take them long to get to level 60 - 65 with them, which is probably more than enough.
However, I would also like to give you some advice on these move sets. I know this is in game, so the moves don't matter that much, but some of these move sets are actually not that good, simply because they have practically no type diversity.
Note: with these move sets I have tried to only recommend TM that you can get before the E4, but it is possible I might have got something wrong and the TM I suggest might only be post-game, which is of course no use to you right. I will still try to avoid doing that, though, but just be aware that I could get it wrong.
Yvetal
You have one Ghost move and two Dark moves on this. Keep Dark Pulse and get rid of the other two. Ghost and Dark cover exactly the same types (Ghost and Psychic), and the only differences are their resistances. Since Yvetal is a Dark type it will get STAB on the Dark moves, so it makes sense to use those. Foul Play is only really useful for Pokemon with a low Attack stat, so they might actually be able to do some damage. Therefore I think Dark Pulse is the best option left.
So as a final move set I would suggest:
- Oblivion Wing
- Dark Pulse
- Dragon Rush (learnt at level 63) or Dragon Claw (TM, found in Victory Road)
- U-turn (TM, found in Couriway Town) or Fly, just for the out of battle utility (also good for checking what attacks the opponent has)
Blaziken
This move set is pretty good, but it needs a Fighting move.
E.g.:
- Blaze Kick
- Brave Bird
- Sky Uppercut/Brick Break
- Slash/Shadow Claw - slash doesn't really add anything, so you might prefer Shadow Claw for Psychic types (and thanks to Speed Boost, he will probably be fast enough to move first)
Charizard
It really doesn't need 3 Fire attacks.
I suggest:
- Heat Wave/Flamethrower
- Fly
- Earthquake
- Solar Beam - if your Charizard is holding the y mega stone it will have the ability Drought, so there is no drawback to this, and it gives very good coverage - or give it Brick Break, Shadow Claw, or Dragon Claw instead if you prefer.
Lucario
This is a good move set, but consider replacing one of the Fighting moves with Dark Pulse, so you are not walled by Ghosts.
So:
- Close Combat/Aura Sphere
- Dragon Pulse
- Extreme Speed
- Dark Pulse (get it from the Move Relearner)
Raichu
Again - 3 Electric moves is overkill.
A better idea is something like:
- Thunderbolt/Discharge - only keep Discharge if you want to use it in Double Battles later on, otherwise go with T-bolt.
- Brick Break
- Dig (only use it if you are sure the opponent doesn't have Earthquake!)
- Nuzzle/Thunder Wave - Raichu has a rather limited selection, so maybe take the paralysing options. Alternatively, check what Hidden Power it has - if it is good maybe use that instead.
Greninja
This is OK, but it doesn't need 2 Dark or Water type moves. I can kind of get having bot Hydro pump and Surf at least, because Surf is good for out of battle, but Hydro Pump has more power in battle, but I would suggest keeping one or the other.
- Hydro Pump/Surf
- Dark Pulse
- Extrasensory
- Ice Beam
There are quite a few moves it can learn - check Pokemon DB's page for it. But I think this is the best. Water Shruiken is something else to consider, though, as it is good for Priority and for breaking through Sturdy if you need to (only one Pokemon in the E4 has that, though).
SPOILER ALERT: If you don't want to be spoiled, then don't read on.
Be careful with Raichu. There is a Water type E4 member, and that is really your only strategy against him, as no one else has any Electric or Grass attacks, and only Greninja resists Water type moves.
As you probably expect there is a Dragon type member as well, so keeping the Dragon moves is a good idea, but also Ice Beam is very helpful for that.
As for the other two E4 members, you have several counters to them so they shouldn't be a problem.
The Champion might be an issue, though. Her best Pokemon is a Mega-Gardevoir, and you don't have much that is super-effective against it. None of your Pokemon can get Steel or Poison moves before the E4 as far as I can tell (unless I missed something), besides Lucario's Metal Claw (from the move relearner), but its Base power is so low that I wouldn't bother with it. That just leaves Ghost as the only type you have to hit Super-effectively. If you followed by suggestions then only Blaziken (who also happens to resist Fairy and gets its own Mega Evolution) and potentially Charizard will have a Ghost type attack. If you keep Phantom Force on Yvetal, then that will as well, but as it is weak to Fairy attacks I doubt it will help that much.
Well, I hope this long answer helped, and I also hope I didn't spoil it too much for you with the spoiler at the end.
