I'd say to start over (at least 2 characters) in order to get your melee characters out of the group. 5 boxing is better off if you're running your tank as your main, and you have 4 ranged players backing them up. You could eventually try melee characters, but its ultimately a pain in the ass.

"Conventional" 5 box groups designed for PVE include:
- Holy Priest, (some 3-person combo of locks and mages), +whatever tank you prefer
- Prot Pally, 4x Shadow Priests
- Holy Priest, 4x Warlocks (the pets will destroy all non-heroic instances)

There are a lot more out there, I would only suggest that you stay away from melee at first.