Well, the Pokemon are extremely tough, so you may want to be at a very high level. Maybe 60-70 would be good enough. For each Pokemon, I suggest you go as the opponents weakness, or battle with a friend.
I`ll give all type defenses, so you can have an easier time choosing your Pokemon carefully.
Lugia-Tidal Sound Ruins
Type defenses
Normal- None
fire- None
water- None
electric- 2
grass- 1/2
ice- 2
fighting- 1/4
poison- None
ground- 0
flying- None
psychic- 1/2
bug- none
rock- 2
ghost-2
dragon- None
dark-2
steel- None
Ho-oh-Eternal Tower
Type defenses
Normal- None
fire- 1/2
water- 2
electric- 2
grass- 1/4
ice- None
fighting- 1/2
poison- None
ground- 0
flying- None
psychic- None
bug- 1/2
rock- 4
ghost- None
dragon- None
dark- None
steel- 1/2
Reshiram-White Summit
Type defenses
Normal-None
fire- 1/4
water-1/2
electric-None
grass-1/4
ice-None
fighting-None
poison-None
ground-2
flying-None
psychic-None
bug-1/2
rock-2
ghost-None
dragon-2
dark-None
steel-1/2
Zekrom- Black Edge
Type defenses
Normal-None
fire-1/2
water-1/2
electric-1/4
grass-1/2
ice-2
fighting-None
poison-None
ground-2
flying-1/2
psychic-None
bug-None
rock-None
ghost-None
dragon-2
dark-None
steel-1/2
Kyurem-Sky Tower
Type defenses
Normal-None
fire-None
water-1/2
electric-1/2
grass-1/2
ice-None
fighting-2
poison-None
ground-None
flying-None
psychic-None
bug-None
rock-2
ghost-None
dragon-2
dark-None
steel-2
Kyurem-B-Deserted Sky Tower
Type defenses-same as the regular kyurem
Kyurem-W-Deserted Sky Tower
Type defenses-same as the regular kyurem
(None means no weakness nor strength.
1/2 and 1/4 mean it takes less damage from the attack type.
2 and 4 means it is weak to the attack type
0 means it takes no damage from the attack type.)
