I did it one by one, I only did this to get the extra 20% buff xp potion u can get

TBh I think there is like 5 quests where u had to be seprated from the group, but after that it isnt so bad.

U could just miss the garrison and still collect the treasures and get to 92, I say 92 coz if you dont u will probably need two potions for that. I did the dungeon with 4 toons and my 5th toon that was 110 that boosted me and killed the last boss with ease.
If u doing it with 5 then maybe questing would be better