Aaron
Dustox
Beautifly
Vespiqueen
Heracross
Drapion
Bertha
Quagsire
Sudowoodo
Golem
Whiscash
Hippowdon
Flint
Rapidash
Steelix
Driflblim
Loponny
Infernape
Lucian
Mr Mime
Girafirig
Medicham
Alakazam
Bronzong
Cynthia
Spiritomb
Roserade
Gastrodon
Lucario
Milotic
Garchomp
For the rematches, these are their teams. When you get the national dex, the elite four add one more mon to their teams and they all increase in levels. I will mark them with a * to indicate that this mon is only when you have the nat dex
Aaron
Yanmega
Scizor
Vespiqueen
Heracross
Drapion
Flygon ***
Bertha
Whiscash
Gliscor
Golem
Hippowdon
Rhyperior
Nidoking **
Mamoswine > replacing Golem in nat dex
Flint
Houndoom
Infernape
Flareon
Rapidash
Magmortar
Ninetales
Arcanine > replacing Flaeron in nat dex
Lucian
Mr Mime
Espeon
Bronzong
Alakazam
Gallade
Slowbro ***
Cynthia
Spiritomb
Roserade
Togekiss
Lucario
Milotic
Garchomp
Porygon Z *** > replacing Roserade
Source
Be warned, most, if not, all of them uses competitive movesets, evs, natures and items so if you are not prepared, you are in for a rough fight
