Well, lets see what can happen.
Vs Sidney: PDC's Bug-type moves are very effective here, except that's just...Fury Cutter. I guess there is the Brick Break TM, but that's also useful against Glacia, who enjoys hammering Armaldo with Surf.
Vs Phoebe: Shadow Ball TM. I can use it, and still be immune to her Ghost moves.
Vs Glacia: Brick Break, Iron Tail, Thunder and Fire Blast are all really useful TMs to use here. Make sure the one who verses Walrein is at least Lv. 53; you don't want to lose it to Sheer Cold.
Vs Drake: Blizzard!! Ice Beam!! Everything except Sheldon is 4x weak to Ice moves. Have you been to Shoal Cave? If not, get a Spheal or Snorunt, with preference to Spheal, who is bulkier than Glalie.
Vs Steven: Your Surf user should be used here, as Surf hits half the team for super effective damage (and will still hit Skarmory on its weaker defensive stat). The aforementioned Spheal works well here too, with only Cradily's Giga Drain, Claydol's Ancientpower and Aggron's Thunder (which won't hurt when coming off of 60 base Sp. Attack) threatening it.
General Advice: Pick your 6, and grind to Level 55.