That is't that great at all. Because 2 Melee suck in this game big dinosaur balls (in my Opinion) I mean the autofacing and all that stuff is quite cool but for 2 Melee ?! I had to test it

Priest/ Knight or Vice versa isn't that great too, because both use the same Mana Pool. I'm going to get my Knight something like Rogue or Warrior in addition so the Dmg might get up enough to compensate(hope this word exists) a missing groupmember. My Priest is getting Scout to (the DoT is Insane) So I get more dmg and do not use my Healing mana.

So Finally I get it like this: Main/Secondary

Knight/ Warri or Rogue
Priest/Scout
Mage/Scout

Should be Enough for Dmg output. Ok the Worst case would be all dungeons are designed for 6x Double Classes, what I don't expect because you should be doable with randoms, and 6 Random Casuals (sounds a bit like 1@m teh 1337, but it is like this most of the time) are 3/4 Well expirienced and synchronized noncasuals/nolifers.

That's why I want to add maybe a 4th. So Iam really able to do Instances without Problems. and the 4th will be I guess Priest/Scout (if a druid comes in he will be with the out)

Hope it will work.