If you want the Tank to have most of the threat...
I'd run the tank in Blood Presence and spec'd as a Blood tank.
Then run the others as Unholy or Frost (your preference), either way in Unholy Presence.
It is worth noting, Frost spec currently does a lot more damage than Unholy.

If you don't care who has threat, because they're all in Blood Presence, and with Blood tanking specs...
Then aggro can bounce around, and you won't need a healer often prior to heroics.
Especially with Rune Tap, every 30 seconds.
Death Strikes.
Dual-wielding, for a lot of Blood Worms.
Round-Robin of the taunt key.
The ability to summon and sacrifice your pet.
The option to Lichborne whoever needs the heals and Death Coil them.