I can only assume that your Fraxure is below level 48, because otherwise it'd be a Haxorus by now.
Use your Zorua that you got as a gift from Driftviel; at level 64 it will ruin Caitlin and Shauntal with Night Daze (use Nasty Plot if you want to be sure).
Use your Cobalion (I used a Mienshao) for Grimsley. One Sword Dance Sacred Sword will end him.
For Marshall, I used an Emolga with Acrobatics. Kid you not, it works. I used my starter for Sawk because of Sturdy, since it will use stone edge on your flying Pokemon.
When facing Iris, I do not recommend you use Altaria or Fraxure, because unless they are at a significantly higher level, they will take too much damage from Iris' Dragon Pokemon. Altaria also does not have a high attack stat. Use Cobalion for Aggron, Hydreigon and Lapras, then use a water Pokemon with Ice Beam/ Waterfall for Druddigon, Archeops and Haxorus (I used my Samurott).
Any moveset/ team combination is possible when you're at Level 65+, but if you want to cruise through the E4, take advantage of STAB.