That is going to be challenging.
There are three things that are causing group leveling to be difficult:
Limited content at 50, relieved a bit now by the opening of fear, but past few weeks when I went in a dungeon it was all bored 50's solo camping stuff.
Another is a lack of group bonus. XP is alot faster solo or in duos with people that don't take smoke breaks etc. The TLP servers got this right, you need a bonus to make up for all the overhead of the cat herding and afk people.
And of course, overcrowding. Why invite a 5th or 6th group member when you are all sitting around full mana waiting on stuff to spawn anyway? There's no bonus for it so why split it even more?