Wow! Great idea here. I'll post my thoughts.
Fortree Gym - Winona has Altaria, Pellipper and Skarmory. Ash uses his techniques he learned from Pokering (see Ag 80) to help his Swellow strike as hard as Winona's team. He also uses Pikachu and Grovyle.
Mosdeep Gym - Solrock and Lunatone. Ash may have a rematch as he hasn't had much expirience in 2V2's, especially as Liza and Tate train their Pokemon for 2-ON-2's. I predict Torkoal and maybe Pikachu.
Sootopolis - Hmm I think Wallace will have an almost identical team, except no Luvdisc or Seaking. Ash will OBVIOUSLY use Pikachu, Grovyle and either Swellow or Corphish.
ps: Wow, Drew's mom? Hehe I hope she kicks his butt :-/ I REALLY hope Drew has a different Pokemon this time.