Start the pull, but put a 55-60 yard separation on Shannox and Riplimb. Exceed 60 yards and they both enrage.
Kill Rageface first. The Shannox tank gets hit much harder as a result, but it's easier to deal with that than whatever Rageface will dish out.
AFter Ragefce dies, melee go to Shannox while ranged go to Riplimb.
When Shannox throws his spear, the Riplimb tank immediately runs towards Shannox. This causes the spear and Riplimb to be 30 yards apart when the spear lands, so Riplimb has to run 30 yards just to get to the spear, then another 60 yards to get back to Shannox. If you can slow Riplimb, or even get him in a crystal trap in the path he takes to run to the spear and back, will give both tanks enough time to lose their debuffs. In the event that the Shannox tank doesn't lose his debuff completely, he should still be able to survive until the next spear throw
DPS Shannox down to 35%, then DPS Riplimb down to death, then kill Riplimb, pop Lust and cooldowns, and kill Shannox.