ICC10/25 HC Shambling enrage question

When am i supposed to stun the shambling so it doesn't go berserk. During the 5 second enrage or after? (Same question applies for the shockwave.)
How to manage this with 2 Shamblings?
Any way (or addon) to track the enrage timer on Shamblings and have an easy time target switching between them?
Also, how to have a better view of threat of LK and Shamblings during the mess in first phase.

You save your stun for hard enrage which happens when shambling goes below %20 hp, not dispellable one. You can pre stun it just before necrotic tick and move far away for next ticks to kill it before it reaches you.