You have a stun and holy wrath, you have a DK who can chain it, a hunter who has at least 1 stun and frost trap, a priest who can slow it, a holy paladin who prob has 2 stuns, a dps warrior who can hamstring and if need should have a macro to stance dance and stun, a druid who can slow it, the shaman can slow it and the warrior main tank if need could charge or shockwave or conc blow it given you should all be stacked on each other.
And you want more ways to slow or stun it????
Infact in your group the lock is I think the only one who cant slow or stun it.
As for LK you can simply rotate the tanks after each soul reaper the other tank isnt exactly busy.
** Remember Warcraft players fail in directions you never thought possible.