Elite Four members seem are confirmed. Teams are unknown. Explanations of teams:


Misty: picked her team from GSC, removed Lapras (Lorelei had it), and Quagsire (it didn't have its Ground-type stuff, it didn't also had preevolution so I thought she wasn't going to get that for the moment). Added Water/Steel stage 3 eelfish, Seaking (since Goldeen got a preevo, thought Seaking maybe got more relevance so it could perfectly be in her team), and Politoed (was between this and Slowking. Kingdra was also an option, but Lance). So far the roster which I have most doubts.
Lorelei: Easiest one. I used her RBY roster, reemplacing Slowbro for that new Ice mon. I could have added Delibird for Lapras in Lorelei, and then Lapras in Misty, but for some reason, Delibird in beta was Water/Ice instead Ice/Flying. Also, I'd have doubt Delibird was entering in its roster since it has really crappy stats and gimmick
Bruno: Another easy one. Since this time there isn't Chuck, that means there is nobody important using Primeape or Poliwrath, so Onix/Steelix loses it sense there.
Giovanni: Donphan for Rhyhorn was easy. Steelix for Nidoqueen...I have my doubts, honestly.
Lance: Could have used same roster as GSC one. Here I recognize I've improvised, I'll guess Gamefreak won't be lazy and won't try to repeat Pokemon. Since Clair isn't in the game, nobody important uses Kingdra, so is an easy adition to the team. One Dragonite reemplaced. Final one is my improvisation, and I subbed it for Ampharos (not for its mega stuff, but Ampharos early design, even earlier than this beta, was Electric/Dragon according to one interview. It being in Lance team would be like an eastern egg)