Since you're going to split them up at level 85 anyway, maybe a hunter with the priest + lock. The hunter's tanking pet works very well for leveling up, even when/if he loses ago, it no longer matters since the mob will die before getting to your group. The lock's voidwalker "should" be as good for a tanking pet, but for some reason, just isn't. (too slow).

Even at 85, my hunter's basic bear pet that he's had like forever, works fine. I've enjoyed the survival spec long before it was the flavor or the moment, and see no need for the special beastmaster pets for leveling. For raiding, you might want to dual spec for those special pets.

With this group, led by the hunter, you'll rarely need the priest to heal, so mostly DPS with the priest. With no mage in the group to rip ago off the bear, this group should be able to blast through the levels very quickly! (Arcane mages my not be overpowered while leveling, but they sure "seem" so compared to my other toons while leveling (like usually nearly double the DPS), and insanely easy to macro!)

Good luck, and make it FUN